notes on the topology of vector fields and flows

21
Notes on the Topology of Vector Fields and Flows

Upload: ngodung

Post on 12-Jan-2017

226 views

Category:

Documents


0 download

TRANSCRIPT

Page 1: Notes on the Topology of Vector Fields and FLows

Notes on the Topology ofVector Fields and Flows

!"# ′$&%' )(*+,&-/.0 12435

687 #9:;3=< $>$&%

?A@BC DFE @GH&IJ D @LK+M/NPO/KNQC KRISNQT)IUBNQ@T+B@VJ9TRHW JXCUY@ W J9CZNQB5I\[]JXTH_^&@ D YRJ9^I`T a Y+@ D @ J/IW KBYbJ/INQT]B W ^&KC\J9CZN TRJ9GScKNZHdH;eTRJ W NPB5Ifhgjilknmpoq T D H;@ D C W J9rs@Ih@TRIU@ CZY+@8tuJ/IhCJ W K+TC NQT vD W J9CUN TwCZYJ9CnJxt"@BC D8E @GHB;J9TdB5J D2D e9[ a @8^ D @>Ih@TCyNQTdCUY@>Ih@8T CU@>IzI W @N W ^ D C2J9TCC ^ G | NQB;J9G @>JXCUK D @>IJ9TRH~B TRB@^&C\IFCUYRJ9CFB;J9TM/@nKRIh@>HC n| @CzJ | GQN W ^Ih@ a YRJ9CFJt@BC DE @GHLNIH NQT | o< F 7 #93 ;l t@BC DzE @GZHJ D NIh@>INQTJIUNQCUKRJ9CZN T a Y@ D @>[pD I W @ D @>J/I TR[ACUY@ D @NZIxJH;N D @B2CZN T`JXTHW J | TNQCUKRH;@ J4IIhN | T@>H C @>J9BY ^ NQT+C Ih^AJ9B@ olY@0BGZJ/I\IhNQB@J W ^&GQ@ Jt"@B2C DyE @GZH0NQTCUY@D @>J9G a0D GZHLNZICUY@Lt"@G BNQCUe JIUCU@>J4H;e a NQTRH o@ a NQGPGLH D J a Jt"@B2C DVE @GZH]J/IYRJ9t"NQT | NQC2I^ NQTC D N | NPTJXCCZY+@z^ NQTCnC a YNQBYNQCNIJ/I\IhN | T@>H o&q TCUYNZI a JXeJ0t"@BC DFE @GZH D @>IU@ W M/GQ@>IJ8YRJ9N D H [ a NQCZYJ9GQGjCUY@nYJXN D M/@NPT | ^&@ D @BCUGQexIUC D J9N | YC

i N | K D @ / ?A@BC D i NQ@GZH f KT+T D W J9GPNZ@>H m

R 7 #93;NI[ W J9CZY+@ W J9CUNQB;J9GPGQe9[CUY@BY NPB2@ Jt@BC D*pD @>JXB2Y=^ NQTC J D @ | N T IU^J9B@ oq T | @T@ D JXGZ[GQ@Cy_H;@T CU@J9T ^&@TIh@C 0 KB2GQNH;@>J9TIU^J9B@ ¡ ojf @ a NQGQGKRIhKR

Page 2: Notes on the Topology of Vector Fields and FLows

8 ¢£ CU@>I TCUY@0 ^ G | e ?A@BC D i NQ@GZH&IJXTH i G a I

J9GQGPe£M/@¤NQTCU@ D @>IhCU@>H0NQTxCUY@0B;J/IU@>IRT = JXTHT = ¥ o¦m lY@TJt"@B2C DyE @GZH Tx§NI | NQt@TxM/eJ KTB2CZN T R

→ ¡ o @ a NPGQGJ/I\IhK W @CUYRJ9C

Jt"@BC DdE @GZH NZI¨J9CxGQ@>J/IUC TB@wB TCUNPT+KR KRIhGQe=H;N p @ D @T+CZNZJ9M/GP@>[/H;@T CU@>H g©ªo« D @ | @T@ D J9GQGPe9[ T@B;J9T_JXGZI B TRIhNH;@ D J^&Y@T W @T T¨IhKBYJ/I D @>JXG a NQTRH&[ a YNQBYB;J9TM/@ D @^ D @>IU@T+CZ@>H~M/e¬J­t@BC D®E @GZH a Y+NQBYBYJXT | @>I pD2 W W W @TCC W W @T+C o lY@W JXCUY@ W J9CZNQB5JXGTRJ W @ pD CUYNZI_NI¯#ª &°l;±F;l;# R 7 #93 ; o «J9CZY+@ W J9CUNB;J9GQGQe9[²J³CUN W @>pH@^&@TH@T+Ct"@B2C DE @GZH T®J9T ^&@TIh@Cy´NQTd ¡zNZILJ K+TBCUN T CZY+@ pD WR

× µ → ¡"[ a Y@ D @ µ NZII W @¤CUN W @0NQTCU@ D

tuJ9GjJ≤

C≤

M olYNQTr JVCUN W @>pH;@^&@TRH;@T+Ct"@B2C D£E @GHJ/IJ W tNQ@>[A@>J9BY pD J W @ a YNQBY¶NZIxJ9T D H;NZTRJ D e£t@BC DE @GZH oq TCUY@>Ih@VT CZ@>I a @ a NQGPG | NQt"@ W D @V@ W ^&YRJ/

IhNILC IUCU@>J/H;e f T T·CZN W @>pH;@^>@TH;@TC m t"@BC DE @GZH&I oi N | K D @ ¸¢£D W JXGQNZ@>H0?@BC D i NQ@GH

¹ 8 º1U1\;3»;#ª 4¼8½&#ª 44 ' 4 °#ª .35& u 1Z1\;3»;#ª &½»#ª f D W D @b^ D @>BNZIh@GPe9[yJ9T¾J9KC T W KRI[ D HNQTJ D e¶H;N p @ D @TRCUNJ9Gj@O/KRJ9CZN T m H;@ E T@>H T¿J9T ^&@T¿Ih@Cy KBGQNZH;@>JXT§IU^J9B@À ¡NI=JXT@O4KJXCUN T CZY+@pD W

a Y+@ D @ q→

H;@T CZ@>I¶J9T¯KTruT a TBK D t"@ ^J D J W @C D NZ@>H M/e I W @ f J/I e"@CKT+rsT a T m NPT+CZ@ D tuJ9G q B T+C2J9NQTNQT | Á [dJ9TRHR

→ ¡NZI g©ªo

 NQt@TJ9Tez^ NQT+C0 ∈

x[ a @ W J9e³J4IIUK W @J9T NPT+NQCZNZJ9G£B TRH;NQCUN T CUY@ pD W f Á m =

0o

dNQCUYCUYNZI³B TRH;NQCUN TR[CZY+@ NZIUCU@TB2@lY@ D @ W pD I GQKCUN TRI J9KC T W KRI³Ã oÄkno oÄÅ IIhC2J9CU@>ICUY@ p GQG a NQT | lY@ D @@NZIUC\I£J8T+K W M/@ D B > Á J9TRHxJVI GPK+CZN T f −B;[5B m

→ o»q T

CUY@ Dxa¤D H&I[² f Á m = 0

J9TRH&[ pD @>JXB2Y¶C8NPTCUY@¤NQTCU@ D tJ9G f −B;[9B m [ a @0YRJ9t"@0 ′f C m = f f C mpmpolYNZInI GQKCUN TNZI¤K+TNQO4K+@=NQTCUYRJ9C8J9TeBK D t"@e f −B;[5B m

→ a YNQBY]J9GI I\J9CUNI E @>ICUY@NQTNZ

CUNJ9GB TRH;NQCUN T¶e f Á m = 0

J9TRHdCUY@@O/KRJ9CUN Te ′f C m = f e f C mpm [ W KRIhClNQT J9BClM/@¤CUY@0BK D t"@¤ olYNQTr F f m J/I D @^ D @>IU@T+CZNQT | CUY@t@G B2NPCUe JIhCU@>J4H;e a NQTRHdJXCCUY@³^ NQTC o lY@T]CZY+@I GPK+CZN TÆBK D t"@b f C m D @^ D @>Ih@TC\IdCUY@bYe"^ CUY@CUNPB5JXGC D JªÇÈ@B2C D e J W J/I\IhGQ@>I\I^AJ D CUNQBGQ@D @GQ@>J/IU@>HVJXClCUN W @ = Á J9ClCUY@¤^ NQTCl

0o

Ã*T+@ W JXe J9GZI B TRIhNZH;@ D °p#°u º1U12;3»;S#ª y&½»#ª o lY@>Ih@VJ D @@O/KRJ9CZN TI CZY+@ pD W

tddx

f x( )=

tddx

f x t,( )=

Page 3: Notes on the Topology of Vector Fields and FLows

¢£ CZ@>I TCUY@¤ ^ G | e ?@B2C D i NQ@GZH&IJXTH i G a I ¥ +

a Y+@ D @] q→

TB2@¶J | J9NQTÆH;@T CU@>IdJXTKT+rsT a T BK D t@^J D J W @C D NZÉ@>H M/e I W @NQTCU@ D tJXG qÉo Ê a @t@ D [ NQT CUYNZI B5J4Ih@>[R

× µ → ¡8NZIJ g© KTB2CZN T)C\J9rsNQT | T C

T@M/KCC a0 J D| K W @TC\I o0fpÊ @ D @ µ D @^ D @>Ih@TC\IFI W @¤NQTCU@ D tJXG CZN W @ oËm IJXeCUYRJ9CjzNZIFJI GQKCUN T JT TRpJ9KC T W KRI8à oÄkno o GPNQrs@=CZY+NI W @>J9TRICZYJXC W KRIhCIJXCUNZI ebCZY+@NPT+NQCZNZJ9GB TRH;NQCZN T[ f CªÌ m = &Ì o TRHnCUY@ D @ W KRIhCy@"NZIhCLI W @nTK W M/@ D B > ÁIhKBYCUYRJ9C pD @>J9BYClGQe"NQT | NQTCZY+@¤NQTCU@ D tuJ9Gf C

0 − B5[XC0 Í B m [ a @]YRJ9t"@]

′f C m = f f C m [XC mpo

f ¢£ CZ@CZYJXCK+TGQNQrs@CUY@NQTCU@ D tJ9G f −B;[\B m NQTVCUY@J9KC T W KRIB;J/Ih@>[ a YNQBY W KRIhCnB TC\J9NPT Á [CUYNZISNQTCU@ D tJ9G W J9e W NQC Á M/KC W KIUCSB TC\J9NQTCUY@¤tJ9GPK+@¤C

0o¦m

lY@¤BGZJ/IIUNQB@J W ^&GQ@ IhKBY¨JXT@O4KJXCUN TxNZIJ | J9NQT a NQTRH uD @>JXG a NQTH>[ a YNQBYtuJ D NQ@>I a NPCUYCUN W @ o lY@ KT+BCUN T f [sC m W J9eM/@=CUY K | YC J/I D @^ D @>Ih@TCUNQT | CUY@zt@G B2NQCZe CUY@ a NQTRHJ9CFG B;J9CUN TJXTHCUN W @nC o TRHVCZY+@ÀI GQKCUN TBK D t"@ D @^ D @>IU@TC\ICUY@C D JªÇÈ@BC D e J^J D CUNPB2GQ@¤CUYRJ9ClNI D @GP@>J/Ih@>H0NQTxCUY@ a NQTRHVJXCCUN W @ = C

0J9ClCUY@¤^ NQTCl

0o

% ÎÏ + ' ±F 7 q TbJ/H&H;NQCZN TC B TB D @CZ@ | @ W @C D NQB5JXGJ9^&^&GQNB;J9CUN TI\[ T@ CZY+@ W IUC*N W ^ D C\JXT+C*KRIU@>I H;N p @ D @TCUNZJXG»@O/KRJ9CZN TIjNZIjC K+TRH;@ D IhC2J9TRH¤CUY@@t GQK+C N T CZY+@IUC\J9CZ@ J9T¨J9M+IhC D J9BCl^&Y+euIhNB;J9GIUeIUCU@ W J4I¤CUN W @=^ D|D @>I\Ih@>I o»i D @J W ^&GQ@>[B TIUNZH;@ D CUY@bY+NPT | @>H D pIhYRJ9^&@>H®GQNHJ9C ^~I W @]^&K+M4GQNQBC D J4IhYB5JXTI oq C2Ix^&Y+euIhNPB5JXGIhC2J9CU@zB5JXTM4@=H;@>IhB D NQM/@>H£M4eC a0 B D H;NQTRJ9CZ@>I CUY@§JXT | KGZJ D ^ IUNQCUN T CUY@GQNH&[zJ9TRHCUY@J9T | K+GZJ D t"@G BNQCUe a NQCUY a YNQBYNQCNI D2 C2J9CUNPT |J9M K+C0NQC\ILYNQT | @ o lY@J9MIUC D J9BC D @^ D @>Ih@TC\J4CUN T J9GQGdIUC\J9CZ@>I¨NZI¿J9BCUKRJ9GQGQeÆJbB2e"GQNQTRH;@ D [M/@B;J9KRIh@0CUY@VJXT | KGZJ D ^ IhNQCZN T D @^&@>J9C\IJ CU@ D

π o lYNZIÐBeGPNQTH@ D []CUY@T NZIÐCUY@ ± Ï ±F 7 pD CUYNZI^ D2 M4GQ@ W o lY@H;N p @ D @TCUNJ9G@O/KRJ9CZN T |" t@ D TNQT | CUY@Ñ^&YeuIhNQB;I CUY@C D J/IUY+B;J9TGQNZHz^ D tNZH;@>IJ0t"@BC DE @GZH TÀCUYNZI^&YRJ/IU@IU^J9B@ o D JªÇÈ@BC D NQ@>I CZY+NIt"@B2C DE @GZH=H@B D NQM4@zCUY@BYJXT | @nNQTIUC\JXCU@nCUYRJ9CFCUY@nGQNZH a¤ KGZH@^&@ D NZ@TB2@ pD W JXT+eNPT+NQCZNZJ9GS^ IhNPCUN T osÒ YeIUNQB5JXGQGQeX[CUYNZINZI¨CUY@BGZJ/I\IhNQB ^&@TRH;KGQK W a NQCZY pD NQB;CUN T oi N | K D @ ¥ Ò @TH;KGQK W a NQCUY i D NQBCUN T

q TÓCUYNZI E+| K D @§CZY+@§Y D NZ TC\J9GB D H;NQTRJ9CZ@D @^ D @>Ih@TC\IÔCZY+@ÕJ9T | KGZJ D ^ IUNQCUN T f a Y+NPB2YYRJ/IzM4@@T¿KT D GQGP@>HC GZJ9eCUY@ÀBe"GQNQTRH;@ D KCcRJ9C\ÖY@TB@ CUY@ ^&YRJ/Ih@^ D C D J9NQC J9M t"@D @^&@>J9C\I a NQCUYÐY D NZ TC\JXG=^&@ D N H π mpo lY@t"@ D CZNQB;J9GB D H;NQTRJ9CU@ D @^ D @>IU@T+C2ISCZY+@VJXT | KGZJ Dt"@G B2NPCUe9[ CZY+@C D J/IUY+B;J9T³GQNH oi D J9TeLNQTNQCUNZJXGB THNQCUN T N o @ o [¾J ^ NQT+C CZY+NIÑ^&YRJ/Ih@Ih^AJ9B@ CZY+@¤K+TNQO4K+@¤C D JªÇº@BC D e£CZY K | YxCUYRJ9C^ NQTCIhY a ISCUY@zCZN W @z@t GQKCUN T CZYJXCSNPT+NZCUNJ9GlB TRH;NQCZN T oAq CNZI£JX^&^J D @T+C pD W CUY@ E+| K D @xCUYRJ9C\[ pD J9G W IhCnJ9GQG*NPT+NQCZNZJ9GB TRH;NQCZN TI\[CUY@C D JªÇº@BC D eÐ@t"@TCUKRJ9GQGQe¬Ih^&N D J9GZI¿NQT+C JIhC2J9CUN TJ D e¿^ NPT+C CZY+@)t@BC DE @GH o lY+NI

Page 4: Notes on the Topology of Vector Fields and FLows

×8 ¢£ CU@>I TCUY@0 ^ G | e ?A@BC D i NQ@GZH&IJXTH i G a I

B D2D @>IU^ TH>IC |" NQT | CZY D K | Y`I W @ E T+NQCZ@TK W M/@ D*s KGQG D @t GQKCUN TRIjNQTJ9T | KGZJ D ^ IhNCUN T[J9TRHwCUY@TØI a NQT | NQT | M+J9BrÆJXTH pD CUYR[J9^&^ D2 JXB2YNQT | CZY+@ IUC\J9CZN TJ D eÑ@O/KNQGQNPM D NQK WIhC2J9CU@=NPTCZY+@=GPN W NQC o T+e T@ a Y YRJ/InIUBNQ@TCUN E B;J9GQGPe¾@^&@ D N W @T+CZ@>H a NQCUY¯CZY+NI]rsNQTRH C D J/IUY+B;J9TÀrsT a ICUYRJ9CSCUYNZINZI@uJ/J9BCUGPe a YRJ9CYRJ9^&^&@TRI oÙ F 7 #93 ;l ↔ 68Ú Ú ¼ ÚÛ q T¨J W J9CUY@ W JXCUNQB;J9GlIU@TRIh@>[9t@BC DyE @GZH&IJ9TRHH;N p @ D @TCUNZJXG0@O/KRJ9CZN TI W JXeM4@B TRIUNZH;@ D @>HC M/@CZY+@IJ W @CUYNQT | o « D @^ D @BNZIh@GPeX[ÜCUN W @>NQTRH;@^&@TRH;@TCt"@BC D®E @GZH&IJ D @¾CZY+@ØIJ W @CUYNQT | J/IJ9KC T W KRI D H;NQTRJ D e¬H;N p @ D @TRCUNJ9Gs@O/KRJ9CUN TRI olYNZI0NZIIhN W ^&GQeM/@B;J9KRIh@x@>J9BY T@NZIH;@CZ@ D W NPT+@>HM/eJ K+TBCUN T L

→ ¡ o  NPt@TÝJ

t"@B2C D E @GH H;@ E T+@>H M/e J K+TBCUN TR

→ ¡"[ T@ W J9e a0D NQCU@VCZY+@H;N p @ D @TCUNZJXG

@O/KRJ9CZN T | NQt"@TM/eÝH;"Þ H;C = f mpo TRH)B TRt"@ D IU@GQe9[ | NQt"@T¨J8H;N p @ D @TCUNZJ9Gs@O4KJXCUN TH;"Þ H;C = f m [ T+@ W J9eÔ@"C D J9BCCUY@¶t@BC DE @GZH f mpo lY+KRI­M CZY t@BC DÆE @GZH&IØJ9TRHJ9KC T W KRI D H;NQTRJ D e H;N p @ D @TCUNZJXG¶@O4KJ4CUN TIRB;J DD e£CUY@nIJ W @0NQT pD W J9CZN T o TRH IhN W NQGZJ D GQeX[ CUN W @>pH@^&@TH@T+C t"@B2C DE @GZH&I W J9eM4@CUY K | YC J/IjCUY@nI\J W @¤CZY+NPT |J/IRT TpJXK+C T W KIH;N p @ D @TCUNZJXGu@O/KRJ9CZN TI @>J9BY T@¤NZIH;@CU@ D W NPT+@>H0M/e=J KTBCUN TR

× µ → ¡ o

ß yà¨?A@BC D¾E @GH&IáJ9TRHH;N p @ D @T+CZNZJ9G@O/KRJ9CZN TI| NQt@ D NZIU@³C ³ J W NQGQNP@>I C D JXTI pD W J9CZN TI Ih^AJ9B@0B;J9GQGP@>H¤â4à oãl@C*KRINQTC D H;KB2@£T@ a T C\J9CZN T pD CUY@£C D J/Ǻ@BC D e JÝ^ NQTC^ CUY@áI GQKCUN T¯BK D t"@

a Y+NPB2Y=C2J9rs@>IjCUY@tuJ9GQK@^J9C²CUN W @ = Áa NQGQG&M/@H;@T CU@>H0M/e

α ä olY@>Ih@0C D JªÇÈ@B2C D e KT+BCUN TI

α ä W KIUC\[ a Y@ D @H;@ E T+@>H>[FI\J9CUNZI eCZY+@ KTH>J W @TC\J9G 7 4 °#9; 79å)7 u #ª ãl@C^

∈ØJ9TRHLGQ@CIJ9TH

CyH;@T CU@8J9TeC a¤ GP@T | CUYRI CUN W @ o lY+@T=CUY@D @>IhKGQC ¤p GPG a NPT | CZY+@C D JªÇº@BC D e ^ pDCUN W @I\["J9TRHCUY@T p GQG a NQT | CUY@C D JǺ@BC D e CUYRJ9C D @>IhKGQC pD CUN W @VC\[>NZI@uJ9BCUGQeCZY+@IJ W @J/IFCUY@ D @>IUK+GQC v GQG a NQT | CUY@nC D JªÇº@BC D e ^ pD CUN W @nI Í C oq T W J9CUY@ W JXCUNQB;J9GLGZJ9T | KJ | @ ãl@C³O`H;@T CU@CUY@n^ NQTC

α ä f I m [/CZY+@ D @>IUK+GPC Rp GQG a NPT | CUY@C D JªÇÈ@BC D e ^ pD CZN W @wI o lY@T a @ W KRIhCYRJ9t"@

α æ f C m = α ä f I Í C mpoq CxNZIKRIh@ KG£C KTN eCUY@wC D JǺ@BC D e KT+B;CUN TI

α ä pD J9GQG>^NQTC T@IUNQT | GQ@ KTB2CZN T C a¤ tuJ D NZJ9M4GQ@>I oRi D JXT+ew^

∈ J9TRHC

∈q äH;@ E T+@

φ([C m C M/@

α ä f C mpo ¢£aφf ^[9C m NZI+ǺKRIhC

CUY@ D @>IhKGQC p GQG a NQT | CUY@ÀC D JªÇÈ@BC D e ^pD CZN W @¤C olY@TØCZY+@®B TRIhNZIUCU@TBe`B TRH;NQCUN TÐM/@B W @>IǺKRIUCa Y@ D @t@ D NPC]NIbH;@ E T@>H ozf ¢£ CZ@§CZYJ9C)CZY+NZIY GZH&I pD T@ | J9CZNQt@J/I a @GQGJ4I^ IUNQCUNPt@VtJ9GK@>I I JXTH C oËm @ J9GI YRJ9t"@

pD J9GPGs^VNPT oçye³CZY+@ a J9e9[CZY+@@NIhCU@TB@JXTH8KT+NPO/K@T+@>I\ICUY@ D @ W pD Ã oÄkno oÅ ILJ9GZI CU@GQGIFKRIFCZYJXCyCUY@c a¶ KTB2CZN T

φ CUY@C a¤ tuJ D NZJXM/GQ@>Ij^JXTHC

W KRIhCuM4@B TCUNQTK KIUGQe£H;N p @ D @TCUNZJXM/GQ@>[ D g©o¢£a´a @=B5JXTbIh@@=CUYRJ9C pD @>J9BY E "@>HxtuJ9GQK@ C2[ÜCZY+@ D @NIyJ W J9^>^&NQT |z C NQC\IU@G sa Y+NPB2YC\JXru@>In^C

φf ^A[lC mpo lY+NI W J9^&^>NQT | NZI CU@T

H;@T CU@>HÐM4eφ è o lYKRI[³M/e H;@ E T+NQCZN TR[ a @

φ φ p s,( ) t,( ) φ p s t+,( )=

φ p 0,( ) p=

Page 5: Notes on the Topology of Vector Fields and FLows

¢£ CZ@>I TCUY@¤ ^ G | e ?@B2C D i NQ@GZH&IJXTH i G a I é +

YRJ9t"@φ è f ^ m = φ

f ^A[C m a Y+@ D @t"@ D CUYNZINIH;@ E T+@>H oi NQTRJ9GQGPe9[ a @¨B;J9T~H;@ E T@ a YJXCNZI W @>JXT+CnM/e# Ï ¤âàê 7 #9&³àx # Ï =u º1U1\;3»;#ª 4&½»#ª lY+NINZIlCUY@ J W NPGQe JXGQGÀCZY+@C D J9TRI pD W J9CUN TRI

φ è →

o lY+@³B TRIhNZI\CU@TBeB TRH;NQCUN T pD CUYNZI³c a B5JXTÔT a M/@IhC2J9CU@>HJ4I

φ ëì φ è ≡ φ ëZí;è pD JXGQGzIxJ9TRHC pDa Y+NPB2Y¿CUYNZINI=H;@ E T@>H ok K@C CUY@À@O/KNQtJ4GQ@TB@ H;N p @ D @T+CZNZJ9Gy@O/KRJ9CUN TI=J9TRHt@BC DE @GZH&I[;CUY@c aÔ CUY@=H;N v @ D @TCUNZJXG@O4KJXCUN TH;^&ÞîH;C = f ^ m NZIVJ9GZI B5JXGQGQ@>HÀCZY+@xâ4à 1z# Ï R 7 #93; f ^ mpoï 7 4R;35ð;#Ô#3»ÜñX 7 #93¸ &Æ41¾ .LòR 7 #93;lY@KT+NPO/K@T+@>I\I I GQKCUN TIC à okno oÄÅ ICU@GPGZInKRInN W ^ D C\J9TC8NQT pD W J9CZN TJXM KC8CUY@B T E| K D J9CZN T C D JªÇÈ@B2C D NP@>I J g© t@BC DE @GZH Ð J9BY¿^ NPT+C0^ CUY@H W JXNQTêGQNQ@>I T T@nJ9TRH TGQe T@¤C D JªÇÈ@B2C D e oq Tx^AJ D CUNQBK+GJ D [XCUYNZIlCZ@GQGZIlKRIlCUYRJ9CjC D JªÇÈ@B2C D NP@>IB;J9T=T@t@ D C D KGQezB T+t"@ D| @>[ÜB D2 I\Ij@>J9BY CZY+@ D [D M D J9TBY of a¤ C D JªÇÈ@BC D NQ@>I W J9e]4±l±F&3C B T+t"@ D| @>[ vD @J W ^&GQ@>[AN J/ICUN W @

→ ∞M CZYC D JªÇÈ@BC D NQ@>IJ9^>^ D2 JXB2YxCUY@nIJ W @¤^ NQTC oçyKCCUYNZIB;J9T TGQe BBK Da Y+@TÀCZYJXCS^ NPT+CNZINQT J9BCNQC\I a TÑC D JªÇº@BC D e JØIhC2J9CUN TJ D e^ NQTC oËmq CyNZIF@TGQN | YCU@TNQT | C IU@@ a YRJ9CyB;J9TYRJ9^&^&@Ta Y+@T a @dH D ^CUY@=B TRH;NQCZN T]CUYRJ9CCZY+@=t"@B;C DE @GZH¤M/@¤B T+CZNQTK KRIhGPexHN p @ D @T+CZNZJ9M/GP@ o TNQTCU@ D @>IhCZNQT | @uJ W ^>GQ@ fpi N | o × m B;J9T­M/@wB TRIhC D KBCU@>H¤N Jt"@B2C DE @GZH¤NIFH;@ E T@>H TJXGQG ótNZJ0? f [;e m = f [ ¥ e»óUôöõ mpo5f lY@³H;@ D NPtJ9CZNQt"@∂f ¥ e&óhôöõ m Þ

∂eNI e − © ô÷õ9[ a YNQB2YÔH @>IT Cz@"NZIhC

a Y+@Te = Á [I CUYNZIyt"@B2C D¤E @GZH8NZIT CB TRCUNPT+K KRIhGQexHN p @ D @T+CZNZJ9M/GQ@ o4m

ãl@CÔJ¾M/@¯J9TeÐTK W M/@ D o lY@TÕCZY+@BK D t"@| NQt@T¨M/exC

→f C2[ f C − J m õ m NZI£J¤C D JªÇÈ@B2C D e

CUYNZIt"@B2C DLE @GZH o çK+CzIUNQT+B@n? f u[ Á m = f [ Á mpD J9GPGu["NQC*NZIBGQ@>J D CZYJXCCZY+@£pJXNZINPC\Ih@G NZIJ9GZI J¤C D JªÇº@BC D e9[XtNZJCZY+@¤BK D t"@ | NQt"@TM/eC

→f C\[ Á mpo lY+@>IU@ÓC a0 C D JªÇÈ@B2C D NP@>I§B D I\I

@>J9BY CZY+@ D o CjCZY+@^ NQTC a Y@ D @CUY@eB D II\[XC a¤ H;NZIhCZNQTB2CC D JªÇÈ@BC D NQ@>I§IhC2J D C pD2 W CZY+@¯IJ W @NQT+NPCUNZJ9GB THNQCUN TRI o lYNZIyt"N GZJ9CZ@>IyCUY@K+TNQO4K+@T@>II I GPK+CZN TRI a YNQBY W KRIhCxY GZH pD g© t"@BC DE @GZH&I oi N | K D @ × ?A@BC D i NQ@GZH0? f u[9e m = f [ ¥ e»óUôöõ m

Page 6: Notes on the Topology of Vector Fields and FLows

ø ¢£ CU@>I TCUY@0 ^ G | e ?A@BC D i NQ@GZH&IJXTH i G a I

ù Ï Lâ4àÕ18 &3R 7 #93;q TCZY+@ÀB;J/Ih@ a Y+@ D @]Jt"@BC DVE @GZH T ¡xNZIH;@ E T+@>HM/e=J W J9C D NQu[ÜCUY@TxCUY@ D @NZIFJ£IhN W ^&GQ@@"^&GQNQBNQC pD W KGZJ pD CZY+@¤c a® ? oú K^&^ IU@? f ^ m = ãl^J9CA@>J9BY³^ NQTC^[ a Y@ D @ãNZIFI W @¤T × T W J9C D NQ o lY+@TxCZY+@c ab ?NZI| NQt@TwM/eJxt@ D ewIUN W ^&GP@JXTHM4@>J9KCUN KG pD W KGZJ φf ^["C m ≡ @ èvû ^ oÊ @ D @CUY@8@"^ T@T+CZNZJ9G@ü J9TdT × T W JXC D NQ³NZIyCUY@8T × T W J9C D NQH;@ E T+@>HJ4I

ý .*ª º 7 4#ª ¶1Rùj3»XñX 7 #935 &@J D @³T a NQT¶JV^ IUNQCUN T)C W J9rs@J9T)@GQ@>W @TC\J D eB2GJ/IIUN E B5JXCUN T CUY@³rsNQTRH&I C D J4Ǻ@BC D NQ@>IjCUYRJ9CjB;J9T B2BK D o @ W J9ezCUYNQTr JC D JªÇÈ@BC D e¶J4IJ W J9^&^&NPT |

→ ¡ pD WCUY@ D @>JXG]TK W M/@ D I®C Ð K+BGQNZH;@>JXT IU^J9B@ ©ªo

ù Ï ; 4Ó1¿# Ï 3»& 7 u #ª 4®#Ï 4lþ m lY@ W JX^&^&NQT | NI T@>·C £ T@ osq TCZY+NIB;J/IU@CUY@ C D JªÇÈ@B2C D e NZI J BK D t@ CZYJXCÕT@t@ DD @CUK D TRI²C a Y@ D @NPCYJ4I²M/@@T o lYNZINZI²B;J9GQGQ@>HJV3sð+43À#ª3»XñX 7 #93 å osf « D @J9M K+CCUY@>Ih@GZJ9CZ@ D oËm m lY@ W JX^&^&NQT | YRJ/IFJGQ@>J4IhCl^>@ D N Hnÿ Á [4IJXeCÌX[AJ CU@ DLa YNQBY¨NQC D @^&@>J9C\I@JXB2CZGQe a Y@ D @NPCYRJ/I£M4@@TM4@ pD @ f C Í CªÌ m = f C m pD J9GQGFC olY@C D JªÇº@BC D e W KIUC pD W JdIUN W ^&GQ@xBG IU@>HBK D t"@NQT KB2GPNZH;@>J9TáIU^J9B@ o ú K+BYáJC D JªÇÈ@B;

1. In these notes, we will often not distinguish trajectories whicharise from different initial conditions but constitute the same setof points.

eM Mk

k!k 0=

∑=

C D enNZIB5JXGQGQ@>HxJ 7 &]3¸: # o5f « D @=J9M KCCUY@>Ih@¤GZJXCU@ D o¦m

¥ m lY@C D JǺ@BC D e³IUC\J9euIj^&KC o lY+@@TCUN D @C D J/Ǻ@BC D eÀNI8JIUNQT | GQ@³^ NQTC f C m = ^ pD JXGQGC olYNZILYJX^&^&@TRI³JXC0G B5JXCUN TRI a Y@ D @CZY+@t@B;C D¤E @GZHnNI[+JXTH8T a Y@ D @8@GIh@ o lYNZIFrsNQTRH C D JªÇº@BC D eNZIB;J9GPGQ@>H³J#94#ª 3 å ±F # of « D @nJ9M K+ClCZY+@>IU@0GJ9CU@ D o¦mù3¸¨ 4ð å þlÃ*CUY@ D CU@ D W I pD JIUC\J9CUN TJ D e^ NQTCjNQTB2GPKH;@&½&S º :3¸ º¶[" ðS3»° º# å [&ѱ º#[J9TRH!3s o8fhq C¿NIÔJ9GZI I W @CUN W @>IB;J9GQGP@>HÓJ B D NQCZNQB5JXGd^ NQTC\[ M/K+CCUYNZI0CZ@ D W NI0^&@ D YJX^I0M/@>IUC D @>IU@ D t@>H pD NQC\ID N | NPTJXGjH;@ E TNQCZN T 9a Y+@ D @¤CUY@nH;@ D NQtJXCUNQt"@ I W @ W J9^&^&NQT | C © tJXT+NIhY@>I oËm t"@BC DE @GZH a NQCUY KCIUC\J9CZN TRJ D e­^ NPT+C2INIB;J9GQGP@>H4°p ºð+3 o

' ¼S#ª 4 .¤ 7 ;±l#9 1ù±Fªð åú W @ K+TRH&J W @T+C2J9G+B T+B@^&C\I C ^ G | enNQT KBGQNZH;@>JXT´IU^J9B@) ¡CUYRJ9C a NQGPG0M/@KIU@>H DJ/I\IhK W @>H0Y@ D @¤NQTBGQKH@0CZY+@ p GQG a NQT | T ε ; ºð Ï :43 Ï + J¶^ NPT+C^ pD JTK W M/@ D [zH;@T CZ@>H ¢

εf ^ m [NICZY+@ÔIh@C J9GQG

^ NQTC\IJXCFJ8H;NZIhC2J9TB2@ < ε pD2 W ^ o ^ NPT+C^NILJ º º#±F # f D 7/7 °#ª `±F # m J¨IU@C`N pD @t@ D e ε > Á [¢

εf ^ m − B TC\JXNQTRI£J9CGP@>J/IhC T@^ NQTC o

T~±F;Ñ;#NIJ9TeÝIh@CVCZYJXCVNZIJ9TáJ D M/NZC D J D e8K+TN T Ih@C\I CUY@ pD W ¢

εf ^ mpo ¢£ CZ@

CUYRJ9ClCUY@0@ W ^&CUexIh@ClNZI ^&@TR[/J/IRNZIRCUY@0@TCUN D @Ih^AJ9B@0 ¡ o

Page 7: Notes on the Topology of Vector Fields and FLows

¢£ CZ@>I TCUY@¤ ^ G | e ?@B2C D i NQ@GZH&IJXTH i G a I +

7 &Ih@CLNZI³J9TeIU@C a Y Ih@B W ^&GQ@>W @TCb ¡ − NZI ^>@T o O/KNQtuJ9GQ@TCUGPe9[JBG Ih@>HxIh@C*NI0J9TeIh@C a YNQBYB TC\J9NPTI¤J9GQGANPC\IGQN W NQCl^ NQTC\I o ; ºð Ï :3 Ï Jz^ NQTC^NZIJ9Te ^&@TIh@ClB TC\J9NPT+NQT | ^ o Ih@CFNPT¨ ¡£NZI 7 ±F 7 #¤N NQCFNZIBG IU@>HJXTHM KTRH;@>H o Ih@C)NIyu 7 7 #9&³N CUY@ D @@"NZIhC²C a¤H;NZIvÇ NQTC ^&@TIU@C\I\[@>J9BY ja Y Ih@NQTCU@ D Ih@B;CUN T a NQCZYÓNZIT T·@ W ^&CUe o Ih@CxNZI 7 ° 7 #9& N NPC NZI T C H;NZIhB TT+@BCU@>H oq TCUKNQCUNPt@GQe9[]NZIRB T+T@BCU@>H0N NPClNZIJ9GQGsNQT T@ ^&NP@B2@ o Ih@O4K+@TB@Ñ^ © [^ ó [ oËo¦o [^÷[ oËo¦o 4±l±l3» 7 Ï ># Ï n ¨ #^N jpD @t"@ D e ε > Á ["CZY+@ D @@"NZIUC\IJ9T¨NPT+CZ@ | @ D « = « f ε) > Á [IhKBY¨CUYRJ9CFN ≥ «N W ^&GQNQ@>IlCUYRJ9Cj^ GPNQ@>IlNQT ¢

εf ^ mvo lY+NZIFIUNQCUKRJ9CZN T

NZIH;@T CZ@>HM/e)GQN W ^ = ^ ojfhq e K¾J D @T C J W NQGQNZJ Da NQCUY­CUYNZIH;@ E TNQCUN TR[*NQCNZI a¤D CUYC\JXruNPT | CZY+@CUN W @C KTRH;@ D IUC\J9TRHNQC oËm ¢£ CU@CUYRJ9CJ³Ih@O4K+@TB@B;J9T]J9^&^ D J9BYJXC W IUC T@GQN W NQC\[J9GQCUY K | Y´J¶IU@C ^ NQTC\I W J9eYRJ9t"@ W JXT+e o W J9^&^&NQT |£ → ?~M/@C a @@TC a¤ ^&@TIh@C2I0 J9TRH?­NZI 7 #ª 4N ya Y@T+@t"@ DCUY@ D @=J D @z^ NPT+C2I JXTH^=NQTÀ pDa YNQB2YGQN W ^ = ^[5CZY+@TGQN W f ^ m = f ^ mpo5fhq TM D NQ@ U JB T+CZNQTK KRI KT+BCUN T NZI T@ a YNQBY ^ D @>Ih@ D t"@>IRGQN W NQC\I oËm Ï 4&43¸± Ï D #9±F4ð+ 7 &½» º; 7 zM/@C a @@TC a¤ IU@C\IÝJXTHwNIJ W JX^&^&NQT | Y → CUYRJ9CNZI¤B TCUNQTK KI\[ T@>·C T@>[ TC [êJ9TRH YJ4I B TCUNPT+K KRINQTt@ D IU@`Y ©ªo ^ G | e~NZIB T+B@ D T@>H a NQCZY^ D ^&@ D CUNQ@>I IhYRJ9^&@>I CUYRJ9C D @ W J9NQTKT+BYRJ9T | @>H0KTH@ D Y W @ W D ^&YNZI W o

a0 t"@B2C DE @GZH>I D c a I¤J D @£B5JXGQGQ@>Hz#±F°4ð 7 È å >½» Rª;# f D Y W @ W D ^&Y+NPB mN CUY@ D @_NZIØJÓY W @ W D ^&Y+NI W M/@C a @@TCUY@N D H W JXNQTRI a Y+NPB2Y³B;J DD NP@>IjC D JªÇÈ@BC D NQ@>IjC C D JªÇÈ@BC D NQ@>I[/J9TRH0^ D @>IU@ D t@>IRCUY@H;N D @BCUN T NQTB D @>J4IhNQT | CUN W @ o

yl;#9# Ï &43»; 1 68Ú Ú ¼ Ú q TÓJÔIh@TRIh@>[FBG Ih@>H D M/NQC2IJ9TRH`IhC2J9CUN TRJ D e^ NQTC\IJ D @ W KB2Y D J D @ D CZYJXT D @ | KGZJ D C D JǺ@B;C D NQ@>I\["J9CGQ@>J/IUC vD W IhCt"@B2C DE @GZH&I o"q ^NZIJb^ NQTC TÕJ D @ | KGZJ D C D JǺ@BC D eX[ a @ÝB;J9TIhC2J9CU@ @JXB2CZGQe a YRJ9CØT@>J D M/e C D JªÇÈ@B2C D NP@>IG r³GQNQrs@¤NQT¨I W @0T@N | YM D Y H ^ où Ï &3»; q ^§NZI]J^ NQTC TÓJ D @ | KGZJ DC D JªÇÈ@BC D e9[¸CUY@TCUY@ D @NZI¤JT@N | Y+M D Y H£ ^J9TRH¿JY W @ W D ^&Y+NI W Y

→ ¡

a Y+NPB2Y´B;J DD NP@>Id@>J9BY´^&NQ@B@ JC D JªÇº@BC D eGQe"NQT | NQT T+C J8IhC D JXN | YClGQNQT@0NQTx ¡^J D JXGZGQ@GsC CUY@¤pJXNZI oq T®^&GZJXNQT T | GQNIhYR[jCUYNZICZY+@ D @ W I\J9euICZYJXC&3±F #)1d3»;ð+3#ª3»Üñ9 7 #943 å -#ª3»XñX 7 #935 &8ȱá±F 7 À §# Ï ]ਠå # Ï #*±F3»4 ;A º&0l[XC ^ G | NPB5JXGQGQeIh^>@>J9rsNQT | o ± Ï °+4 6 ;ðR°·È º¨ # ' ;#9@ a NZIUYxC H@ E T@Y a J D @ | KGZJ D C D JªÇº@BC D e f C m M/@YRJ9t"@>IJ/ICJ9^&^ D J9BY@>I8NQT E T+NPCUe o ú a @ÆH@ E T@ÔCUY@á;ðR°·È º º#`#`1# Ï #ª3»XñX 7 #93 å ÀC M/@dJXGQGSCZY IU@=^ NQTC\I CUY@H W JXNQT a Y+NPB2YÝJ D @xGQN W NQC\I JdIU@O/K@T+B@ CUY@ pD W f C m pD tJXGQK+@>I CxJ9^&^ D J9BY+NPT |NQT E T+NQCZe o @nH;@T CU@¤CUYNZIIh@ClM/e ωf mpo¼ R4¨±lª>þ g TIUNZH;@ D Jt@BC DSE @GZHNPT a Y+NQBY T@C D JªÇÈ@BC D eJX^&^ D J9BY+@>IJ8B2G Ih@>H D M4NQC

Page 8: Notes on the Topology of Vector Fields and FLows

! ¢£ CU@>I TCUY@0 ^ G | e ?A@BC D i NQ@GZH&IJXTH i G a I

M/e`Ih^&N D J9GPNQT | J D KTHNQCxB2G Ih@ D J9THBG IU@ D olY@TdCZY+@@TCUN D @BG IU@>H D M/NQCNIyCUY@ W @ | J/GQN W NQCFIh@C o¼ R4¨±lª>þ g TIUNZH;@ D CUY@t"@BC DE @GZH? f u[e m= f −u[ue m NPTwCUY@x^&GZJ9T@ o RY@xC D JªÇÈ@B2C D e f C mIJXCUNZI eNQT | CZY+@¤NQTNQCUNJ9GsB TRH;NQCZN T f Á m =f &Ì9[9e&Ì m NZI | NQt"@TM/e£CZY+@¤BK D t"@0 f C m =f &̪@ − è [Xe»Ì@ è mpo lY+KRIl@>J9BYxC D JªÇº@BC D eGQNQ@>I TJYe^&@ D M GJ CZY+@ pD W e = r pD I W @tuJ9GQK@ r f J9TRHCZY+NZIFNQTBGQKRH;@>ICZY+@ÀH@ | @T@ D J9CZ@0Ye^>@ D M GZJe = Á J/I a @GQG mvog GP@>J D GQe9[CUY@ TGQeÕC D JªÇÈ@BC D NQ@>I`YJXtNQT | JT T·@ W ^&CUe W @ | J/·GPN W NQCFIh@CFJ D @¤CUY Ih@¤GQeNPT | TCZY+@¤upJ9NI oú N W NQGZJ D GPe9[uCUY@¨JXGQ^&YRJ=GQN W NQCnIU@C\[ J=C D JªÇº@B;C D e f C m [¯H;@T CU@>H¨M/e αf m [lNZIH;@ E T+@>HJ/ICUY@ W @ | J/·GQN W NQCIh@C CZY+@ D @t@ D Ih@>H£C D JǺ@B;C D en f −C mpo&q TCUY@³J9M t"@@uJ W ^>GQ@>[ TGQenC D J/Ǻ@BC D NQ@>IGPeNQT | TÝCZY+@evJ9NIYJXt@¿JT TR@ W ^&CZexJ9GQ^>YJ4·GQN W NQCFIU@C oú K^&^ IU@]CUY@ D @]NZIJT+K W M4@ D CÌ pDa YNQBYCUY@dC D JªÇÈ@BC D e] f C m D @ W J9NQTRInNQTRIUNZH;@JB W ^J9BCIhKMIU@C CUY@H W J9NQT pD J9GQG¤C ≥ CÌ olY@T)CUY@ p GQG a NQT | W KRIUCM4@³C D K@³B TB2@ D TRNQT | CUY@ W @ | J/·GQN W NQCFIh@C m ωf m NZIRT T·@ W ^&CUe m ωf m NZIRBG Ih@>H¥ m ωf m NZIFNQTtJ D NJ9TCFM/e=CUY@nc a f N o @ o [4NQCyNZIJKT+N T C D JªÇº@BC D NQ@>I m [/J9TRH× m ωf m NZIRB T+T@BCU@>H o

$ " º º#0. åR7 &lY@LGPN W NQCRBe"B2GP@LNIJ9TN W ^ D C\J9TCRC ^ G | NQB;J9G @>J9CZK D @ I W @¤t@BC DE @GH&I o

; #ª È º º# 79åR7 Jt"@BC DE @GZH?¿NZIJ0BG Ih@>H D M/NQC g ?¿CZYJXCNZISB TC\JXNQT@>HNQT αf m D ωf m pD I W @C D JǺ@BC D eL ≠ gyoÊ @ D @NZI)J9T¾N W ^ D C\JXT+C D @>IhKGQCJXM KCGQN W NPCBeBGQ@>IRNQTxCUY@0^>GZJ9T@ ù Ï &3»; fpÒ NPT+B;J D$# ·çy@TRH;NQuI T m ú K^&^ IU@?NZIJ¤t"@B2C DFE @GZHLNQT óX[>J9TRHLGQ@CRM/@J¤C D J/Ǻ@BC D e ? o ú K^&^ IU@´CUYRJ9C ωf m NZIbT TR@ W ^&CZe9[AB W ^J9BC\[SJ9TRHB TC\JXNQTRI£T IhC2J9CUN TRJ D e~^ NQT+C o lY@T ωf m W KIUC]M/@ÆJÔBG Ih@>HD M/NQC o]YRJ9C W J9rs@>ICUY@wGQN W NPCB2e"BGQ@w^J D CUNQBKGZJ D GQeN W ^ D C2J9TCNZI*CZYJXC*NQC a NQGPG^&@ D IUNZIUC@t@T]J CU@ DJ8I W J9GQGs^&@ D CUK D MJ9CUN T CUY@0t"@BC DyE @GZH où Ï &3»;þXãl@Cj?M/@8Jt@BC D*E @GZH¤YRJ9t"NQT | JGQN W NQCBeBGQ@ gyo ãl@C? © M/@£JIhK pE B2NQ@TCUGPeVI W J9GQGf NQTwCZY+@ g Ì IU@TIU@ m ^>@ D CZK D MJXCUN T ? o lY@T? © a NQGQGjJXGZI YRJ9t@nJGQN W NQClBeBGQ@ o<% .*ª º 7 4#ª b41&;ª#9& ' #9#ª °3 å ±F4 º#9 IUC\J9CZN TRJ D e^ NPT+CNZI¤B;J9GQGP@>H³ 4#9&]N NZIT C J GQN W NQC¯^ NPT+C ~ CUY@ D IUC\J9CZN TJ D e^ NQTC\I oq CUY@^ NQTC²^8NZIJ9T³NZI GZJ9CU@>HIhC\JXCUN TRJ D e£^ NPT+C Jt@BC DE @GH? f © [9 ó m = f ? © f © [ ó m [? ó f © [Ä ó mpm [ D')(+*-,./*$0/./*$12 = (+'3,4(+*-,. *-0. *-12+. '304(+*-,. *-0. *-12+. '314(+*-,. *-0. *-12+2 [CUY@T a @£B;J9T K D CZY+@ D NQT+t"@>IhCZN | JXCU@£CZY+@=IhC D KB;CUK D @ CUY@C D JªÇº@BC D NQ@>IT+@>J D M4e³M/eV@uJ W NQTRNQT | CUY@ I ·B;J9GPGQ@>H µ JXB M4NZJ9T W JXC D NQ ^J D CUNJ9GH;@ D NQtJXCUNQt"@>I[ µ ? = f ∂?ÄÞ ∂$5 mpo RYNZIW JXC D NQ a NQGQG B K D Ih@§M/@ × NQT_CZY+@ H;N W @TIUN TRJ9GB;J/IU@=J9TRH 3× ¥ NQTCUY@ ¥ pH;N W @TIhN TJXGuB;J/IU@ o]Y@T a @£@tuJ9GQKRJ9CZ@£CUY@ µ J9B M/NJ9T W J9C D NQJ9CCUY@³IhC\JXCUN TRJ D en^ NQTCS^[ a @ M/C\JXNQT]J W JXC D NQa Y IU@)tJXGQK@>IdJ D @)TK W M/@ D I o I a NQCUY´J9Te

Page 9: Notes on the Topology of Vector Fields and FLows

¢£ CZ@>I TCUY@¤ ^ G | e ?@B2C D i NQ@GZH&IJXTH i G a I 6 +

IhKBY W JXC D NQu[ a @ W JXe)B;J9GQBKGZJ9CU@NQC\I@N | @TRtuJ9GQK@>IJ9TRH0@N | @Tt"@B2C D I o; #ª IhC2J9CUN TJ D eÝ^ NQT+CNIB5JXGQGQ@>HÏ å ±F3¸:*4 7 N CZY+@ D @>J9G²^J D C\I CUY@n@N | @TRtuJ9GQK@>I NPC\I µ JXB M4NZJ9T¨J D @nJ9GPGuT TRp@ D o Ye^&@ D M GPNQBnIUC\J9CUN TJ D eV^ NQTC W KRIhCT@B2@>I\IJ D NPGQe£M/@¤NZI GZJ9CU@>H où Ï &3»;þ q ^dNZIJVYe"^&@ D M GQNQB=IhC2J9CUN TJ D eV^ NQTC\["CUY@TdCZY+@C D JǺ@BC D NQ@>IT+@>J D ^J D @H;@CU@ D W NPT+@>HdK^¿C C ^ G | NPB5JXG@O4K+NPtJ9GP@T+B@M/eCUY@LTK W M/@ DF ^ IhNQCZNQt@J9TRHzCUY@LTK W M/@ D T+@ | J9CZNQt@ D @>J9G^J D C\IwCZYJXCCUY@­tuJ D N KRI@N | @T+tuJ9GQK@>IRYRJ9t"@ o

µ KRIhCY a CZ@T¬H @>IdCZY+NZI T TRp@ D¶D @>J9G^J D C B TRH;NQCZN T=Y GZH7 i D CUKTRJ9CU@GQe pD KI\[XNQCNZIdCUY@ D KGQ@¾JXTH®T CCUY@b@B@^&CUN T oq T¬JIh@TRIU@CZYJ9CB;J9TVM/@ W J/H;@^ D @BNZIh@>[\CUYNZI²B TH;NCUN TY GZH&I a NQCUY^ D2 M+J9M/NQGQNPCUe = olYNZICZY+@ D @ W NZIJ D @ W J D rjJ9M/GQ@J9^&^&GQNPB5JXCUN T C ^ G | e¾C CUY@ÔG B;J9GB2GJ/IIUN E B5JXCUN T IhC2J9CUN TJ D e£^ NQT+C2I o BB D H;NQT | C CUYNZIFCZY+@ D @ W [ a @8B;J9TdB;J9CU@ |" D NZ@ J9GQG+M/KCJVIh@C W @>J/IhK D @ Á CUY@NZI GZJ9CZ@>HIhC\JXCUN TRJ D eV^ NQTC\INPT H;N W @TRIUN TI*NQTCU@ D W I ÇÈKIUC ¥ ruNPTH&I M CUYÐ@N | @TtJ9GPK+@>Ia NQCUYÔ^ IhNQCUNPt@ D @>JXG0^J D C\Ö T@)^ IUNQCUNPt@J9TRH T@~T+@ | J9CUNPt@>[ÀJ9TRHáM CUYÕT+@ | J9CUNPt@ o ú N W NZGZJ D GQe9[/NQT ¥ H;N W @TIUN TRICUY@ D @J D @ × H;NZIUCUNQTBCCUe"^&@>I f @"B2@^>C vD CUYRJ9CFIU@C W @>J/IhK D @ Á mpo; #ª º8wNZI0J9TNZI GZJ9CZ@>HIhC2J9CUN TRJ D en^ NQTC^x@>J9BY a Y Ih@T@>J D M/enC D JªÇº@BC D NQ@>I0wI\J9CUNZI E @>I

ωf m = ouf GPCU@ D TJXCUNQt"@GQe9[

pD @>J9BYbT@>J D M/e)C D JǺ@BC D e)u[²CUY@GQN W NPC f C m J/IRC → ∞ NZIR^ oËm

; #ª 3 7 Jt@BC D*E @GZH¤?]NZIJ9TNZI GZJ9CU@>H]IhC\JXCUN TRJ D e¨^ NQT+Cz^ a Y+NQBYNZI=JIhNPT+r CZY+@ D @t@ D IU@>H E @GZH&[ −? o<5< 98&;#ª35 7 .*+ º 7 #ª 1: å ±F;35: 7n' #9#ª 43 å ±F ºS#9ãl@C0?ØH;@T CZ@¨Jxt@BC D8E @GZH a NQCUYÝJxYe^&@ D M GQNPBIhC2J9CUN TRJ D eL^ NQTC^["J9C a YNQBY³CUY@ µ JXB M/NZJXT W JXC D NQ£NZI µ ? = f ∂?ÄÞ ∂$5 mpoù Ï ¹ °pu º; 4 7 &þlY@@N | @TtJXGQK@>I µ ?­J D @£CUY@ D C\I CZY+@O/KRJ/H D J9CZNQBF^ GQe"T W NZJ9G Òlf

λm H@ E T@>HLM/e Òlf

λm

= H;@C f µ − λqÉmpo ú NQTB@CZY+NINZIJ¿O/KRJ/H D J9CUNPB

^ GQe"T W NZJ9G a NQCUY D @>JXG&B @ pE BNQ@TC\I[CUY@ D C\IJ D @³@NQCUY@ D M CZY D @>J9G D @GIh@³CUY@e)J D @=B W ^&GQ@B TǺK | JXCU@>I @>JXB2Y CUY@ D f IJ9e<; Í ãlNJ9TRH=; − ãlNZ[ a Y+@ D @>;êJ9TRHxã`J D @ D @>J9G mpo @B TIUNZH;@ D CUY@0B;J/IU@>I o ç CZY D C\I D @>J9G

J o ç CUYx^ IhNQCZNQt@ 43 7

M o ç CUYxT+@ | J9CUNPt@ 8

B o Ã*^&^ IhNPCU@nIhN | TI lu

o g W ^&GP@£B T4ÇÈK | J9CZ@ D C\I J o ;®^ IhNPCUNQt"@

±l 3»*S3 7 M o ;®T@ | J9CZNQt@

±l 3»* 8¢£ CZ@ lY+@8IU@TRIh@ CUY@8Ih^&N D JXG»NQT=B;J/IU@ o B;J9TM/@H;@CU@ D W NPT+@>H pD W CUY@dIUN | T B2K D G f ? m J9CCUY@^ NQTC^ oq BK D G f ? m*f CZY K | Y+C J/I8CZY+@IhB;J9GJ D O/KRJ9TCUNPCUe ∂? © Þ ∂ ó − ∂? ó Þ ∂ © m NZIl^ I\NQCZNQt@>[uCUY@TwCUY@¨I a N D G a NQGQGM/@B KT+CZ@ D BG Brja NZIh@>[4J9TRHLt"NQB@0t"@ D IJ où Ï % °pu º; 4 7 &þ

Page 10: Notes on the Topology of Vector Fields and FLows

/Á ¢£ CU@>I TCUY@0 ^ G | e ?A@BC D i NQ@GZH&IJXTH i G a I

lY@@N | @TtJXGQK@>I µ ?­J D @£CUY@ D C\I CZY+@^ GQe"T W NZJ9G Òlf

λm H@ E T@>H0M/e Òlf

λm =H;@C f µ − λ

qhmpo ú NQTB@CUYNZInNZIÀJB2KM/NQB^ GQeT W NJ9G a NQCZY D @>J9G0B @ pE BNQ@TC\I[RCUY@)CZY+@ D e @O/KRJ9CZN TI0CU@GQGZI0KI0CUYRJ9C0CUY@ D @¨J D @@NQCUY@ D ¥D @>J9G D2 C2I[ D0¤D @>J9G D CFJ9TRHVJ^JXN Dy B W ^&GQ@B TǺK | J9CU@ D C\I o4g J/IU@0M4e£B;J/Ih@ o GQG ¥ D C\I D @>J9G

J o GQGs^ IUNQCUNQt"@ 43 7

M o ^ IhNQCZNQt@>[ T+@ | J9CUNPt@ +lu f H;N W I o KC\[ NPT m

B o ^ IUNQCUNQt"@>[ T@ | JXCUNQt"@ +lu f H;N W o KC\[ NQT m

H o GQGsT@ | J9CZNQt@ 8

o D @>J9GZ[ B W ^&GP@ B T4ÇÈK | J9CZ@ ^J9N Df J | J9NQTR[*IJ9e?; Í ãlN£JXTH@; − ãlNZ[ a Y@ D @A;J9TRH0ã¿J D @ D @>J9G m

qÉm @>J9G D Cl^ IhNQCZNQt"@ J o ;®^ IhNPCUNQt"@

±l 3»*S3 7 M o ;®T@ | J9CZNQt@

±l 3»*l f KC\[ H;N W I o NQT mqÉqÉm y@>J9G D ClT@ | J9CZNQt@

J o ;®^ IhNPCUNQt"@ ±l 3»*l f HN W I o K+C2[ NQT m

M o ;®T@ | J9CZNQt@ ±l 3»* 8

< ¹ B Ï # ' &2¨±F435#9# :S#: å ±F;35: 7n' #9#ª 43 å Î ºS#9-Cq ?NZIJLt@BC DE @GZH a NPCUY)JLY+e"^&@ D M GQNQBIhC2J/CUN TJ D e¨^ NQTCxJ9C£CUY@^ NQTC£^[CZY+@TCUYNZINZIIhC2J9M/GP@=NQTCZY+@ p GQG a NQT | IU@TIU@ ú K+^>^ Ih@=? ©NZIFJ9T CUY@ D t@BC DE @GZH a YNQB2YxNZIFIhK pE BNQ@T+CZGQe\g© BG Ih@ C ? NQT_JT+@N | YM D Y H ^ of lYNZI W @>J9TRI CUYRJ9C ? © J9TRH NQC\I E+D IhCH;@ D NQtuJ9CUNQt"@>IJ D @³BG IU@=C CZY+@³B D2D @>IU^ THNQT |

tuJ9GQK@>I ?T@>J D ^ o¦m+g T+BGQKRIhN T CUY@0t@BC DE @GZH? © W KIUCJ9GZI YRJ9t"@NPC\I a T]IhC2J9CUN TJ D e^ NQTC*J9C*I W @^ NPT+C^ © T@>J D ^["JXTH K D CUY@ D W D @Ô# Ï #ª3»Üñ9 7 #9435 &¾41w ò &43~± ò#:­#9±Fªð 7 4 å >½» Rª;##9# Ï #ª3»Üñ9 7 #9435 &n1y`&3V± Ú q TM D NQ@ h JG B;J9Gl^&@ D CZK D MJ9CZN T JnY+e"^&@ D M GQNPB³IUC\J9CZN TJ D e£^ NPT+CFH @>IRT ClBYJXT | @¤CUY@0C ^ G | e olYNZIrsNQTH IUC\JXM/NQGQNQCZe NZIB;J9GQGQ@>H ª 7 #ª35 7 #ªS3»*#9:² º# å olYNZINI¯JÓR;3 å N W ^ D C\J9TC­^ D2 ^>@ D CZe Ye^&@ D M GPNQB IUC\J9CZN TJ D e ^ NQTC\I oq C W @>JXTICUYRJ9CwCUY@e a NQGQGIhY a K^NQTRH;@^&@TH@T+C I W J9GQGx@ DD2D I W @>J4IhK D @ W @TCJ/INQTtuJ D NZJ9M4GQe BB2K D NPTCUY@ D @>JXG a¤D GZH o.¤4R;3»; å - å ª#9& #9#ª 43 å±F #±F& ðª 7 £#ª3¸ 7 #ª3»#9°:² º # å ¨#: Ï å ±F;35: 7 o

< % 3»&+°43F &° Î 3»&;35 ð¶F 7 °#93y ;lq T W JXT+e J9^>^&GQNQB;J9CUN TI pD @J W ^&GQ@>[YeH D H;e"TJ W NQB;I CUY@zt@BC DE @GZH&I@TB KTCU@ D @>H a NQGQG CZ@TM4@Vt GQK W @>·^ D @>IU@ D t"NQT | o/fhq TCUYNZILB TCU@C a @KIU@CUY@CU@ D W t GPK W @ C W @>JXT§M CZY D H;NQTRJ D e¿t GQK W @)NQT ¥ H;N W @TRIhN TI¤J9TRHxJ D @>J a Y+@T a @xJ D @ D @ @ D2D NQT | C £H;N W @TIUN TRI oËmçyeáH;@ E T+NPCUN TR[Jt@BC D]E @GH®NZIRÈ&°±l3»&;35+ ºð a Y@T®NQC\Inc a

φ è B;J DD NP@>IJ9Te ^&@TÔIU@C ú NQT¿NPC\I³H W JXNQT¿C J¨IU@C

φ è ( ú )

CUY@nIJ W @0t GQK W @,pD J9GQGsCZN W @>IRC o

lY@B TRH;NQCUN T pD JÀt@BC DVE @GH?áC ^ D @>Ih@ D t"@wt GPK W @wNZICUYRJ9C¨H;NPt f ? m = Á o*fhq T kCUYNZI W @>JXTI ∂? © Þ ∂ © Í ∂? ó Þ ∂ ó ≡ Á Ö5NPT ¥ k NQC

Page 11: Notes on the Topology of Vector Fields and FLows

¢£ CZ@>I TCUY@¤ ^ G | e ?@B2C D i NQ@GZH&IJXTH i G a I +

W @>JXTI ∂? © Þ ∂ © Í ∂? ó Þ ∂ ó Í ∂?EDÞ ∂D ≡ Á o¦mpoi D CZY+NI D @>J4I TR[CUY@§CU@ D W ºR;35ð; 7 >°1U3»&NIKRIh@>HVJ4IJnIUeT Te W pD t GQK W @>·^ D @>Ih@ D t"NQT | o K+TRH&J W @T+C2J9G²C ^ G | NQB;J9G²B TRIh@O/K@TB2@ M/@NQT | t GQK W @>·^ D @>Ih@ D t"NQT | NICZYJXCF]±F;;#1jS º#90RÈ0 å ;R;3LâàÐ#9x±l3»4±F;3 :;#¬41 º#9; 1`M/eCUY@_c a [a Y+@CZY+@ D NQT^ IUNQCUNQt"@ D T@ | JXCUNQt"@0CZN W @ olYNZIwIUC D T | B TRH;NQCZN T´N WW @>H;NJ9CU@GQe D K+GQ@>I KCM CUY]I K D B@>IJ9TRHxIUNQT+rjI pD W B2BK DD NQT |NQTt GQK W @>·^ D @>Ih@ D tNPT | t"@B2C DE @GZH&I o çyKCLNQCNZI@>J/IUeC Ih@@CUYRJ9CÀJ9TeCUe"^&@ I\J/H&H;GQ@NZI^ I\IhNQM/GP@0NPT¨Jt GPK W @>·^ D @>IU@ D tNQT |£E @GZH o.¤;#3sq T H;N W @TIUN TRI[ACUY@ D @NIJXT CZY+@ D N W ^ D C\JXT+CrsNQTH NZI GZJ9CU@>HIhC\JXCUN TRJ D e¶^ NQTC\[0JB@T+CZ@ D o 7 ;#9;38NZIJVIUC\J9CZN TRJ D en^ NPT+CNQT H;N W @TIUN TRI pD£a Y+NQBY¶ &3¸: å #ª3»XñX 7 °#93¸ &3» 7 ª&Ð435:² º#9 Ú lY+@bIhN W ^&GQ@>IhC@uJ W ^&GQ@ JB2@TCU@ D NZICZY+@À^ NQTC f Á [ Á m NPTCUY@Àt"@BC DE @GH | NQt@T¿M4e? f [+e m = f −e9[+ mf KT+N pD W B KT+CZ@ D BG Br a NZIh@ D C\J9CUN T mpolY@z@N | @T+tuJ9GQK@>I CZY+@ µ J9B M/NZJXT W J9C D NPÀJXCJB@T+CZ@ D W KRIhClM4@±l3sL ºð+ º43 å olY@nB T+t"@ D Ih@nNZI4#¤C D K@nNPT | @T@ D JXG q JXT3¸: #ª3»3 å pH;N W @TRIhN TJXGt@BC D=E @GZHYJ/IJ9T NI GZJ9CZ@>HIUC\J9CZN TJ D e_^ NPT+C a NQCUY ^&K D @N W J | NPTJ D e@N | @TtJXGQK+@>I CUY@ µ JXB M4NZJ9TR[sNQCNZIT CRT+@B@>II\J D NQGQeJ¤B@T+CZ@ D o>q CRB K+GH³J9GI M4@JI K D B@ D JIUNQTr f H;K@C T TR·GQNQT@>J D CU@ D W I NQC\IRlJ9e"G D IU@ D NP@>I mpoÊ a @t@ D [0N J9TÕ3»&+°·±l3»&;35 ð_t"@BC DE @GZH£YRJ/I¤J9TNZI GZJ9CU@>HxIUC\J9CZN TRJ D e^ NQTC a NQCUY^&K D @N W J | NQTRJ D e@N | @TtuJ9GQK@>I CUY@ µ J9B M/NZJXT[CUY@TNQC W KRIhCM/@]JÀB@T+CZ@ D f IhNPT+B@CZY+@ TGQe JXGQCU@ D TRJ9CUNQt"@>I I K D B@ D IUNQT+r J D @

@"B2GQKRH;@>HM/@B;J9KRIh@ØCUY@eêB;J9TT CÝ^ D @>Ih@ D t"@J D @>J mpo B2@TCU@ D NISN W ^ D C\J9TCRM/@B;J9KRIh@0NQC^ I\Ih@>I\Ih@>I7 #ª3s º> 7 ¯#ª35 7 #ª3s¯#9:² º° º# å T+eAF3G$H$FIJG$HK$H$G%LM)N¿t"@BC DE @GHCUYRJ9CNZIIhK pE BNQ@TCUGPezBG Ih@ f NPT=CZY+@ g© Ih@TRIU@ m C T+@YRJ9t"NQT | JB2@TCU@ D [ W KRIhCFJ9GZI YJXt@nJB2@TCU@ D olYKIN CZY+@ TGQeát"@BC DbE @GZH&ICUYRJ9CB;J9TJ D NZIU@ NQT I W @ pH;N W @TRIhN TJXGÓIhNPCUKRJ9CUN TW KRIhC)M4@ÆJ D @>J/·^ D @>IU@ D t"NQT | [LCUY@TÓCUY@ TGQeNZI GZJ9CU@>H8IUC\J9CZN TJ D eL^ NQTC\IjCUYRJ9C²B;J9T³YJX^&^&@TJ D @ m IJ/H&HGQ@>IJ9TRH m B2@TCU@ D I o

< Ù ù Ï Î 4 º 7 3»,Ob±çyedCUY@ÀKRIU@ CUY@ Ò NQTB;J D$# W JX^[ a @ W J9eD @>H;KB2@CUY@£C ^ G | e IUK D2D KTH;NPT | C D JǺ@B;C D NQ@>IC J¶O/K@>IhCZN T K+TRH;@ D IhC2J9TRH;NQT | JW JX^ J8I W J9GQGQ@ D H;NZIUr=C JGZJ D| @ D H;NZIUr o@ a NQGQG+B TIUNZH;@ D JLt"@B2C DE @GZH£NQT ¥ H;N W @TRIhN TI o lY@ pH;N W @TRIhN TJXGB;J/IU@>[&M/@NPT | IUN W ^&GQ@ D [ a NQGQG p GQG a®pD W CUYNZI og Y Ih@bJ9Te^ NPT+C=^ÝM/@G T | NQT | C g [J9TRHB TIUNZH;@ D J9Te ^>@TbH;NIhr k a Y Ih@³NPT+CZ@ D IU@B;CUN T a NQCZY¿CUY@ÀB2N D BGQ@ g NZIzCUY@À^ NPT+CL^[J9TRHa Y+NPB2YwNZI0T C0C2J9T | @TC0C CUY@BN D BGQ@ g J9C0^ ofhq TCZY+@ pH;N W @TIUN TRJ9GFB5J4Ih@ a @ a0 KGZHKIU@J9TJ D B¤NQTRIhCZ@>J/H JxH;NZIUr oËm @ W JXedJ4IIUK W @CUYRJ9C k NZIBY IU@TwI CUYRJ9C*CZY+@£t@BC DE @GZHNZIT a Y@ D @0C2J9T | @TClC ko ú K+BY¨J8H;NZIUr f D J D B5[N NQT HN W @TRIhN TRI m NZIB;J9GQGQ@>H]J 7 7 °#ª CZY+@¤c a oçye8CUY@B TCUNQTK+NPCUe I GPK+CZN TIC g© H;N p @ D @TCUNZJ9G_@O/KRJ9CZN TI\[­CUY@ D @ W KRIhC @"NZIhC JI W J9GQGQ@ D HNZIhr k ÌMP"B TC\J9NPT+@>HÀNQT k J9TRHB TC\JXNQT+NPT | ^[ a NQCUYCZY+@ p GQG a NQT | ^ D ^&@ D CUe

Page 12: Notes on the Topology of Vector Fields and FLows

98 ¢£ CU@>I TCUY@0 ^ G | e ?A@BC D i NQ@GZH&IJXTH i G a I

i D J9Teá^ NQT+C]OÆNQT k Ì9[CUY@ D @`NZIÝJI W J9GQGQ@>IUCVtJXGQK+@ C = C f O m > Á IUK+BYCUYRJ9C p GQG a NQT | CUY@³C D JǺ@BC D e ^ pDCUN W @nC f O m D @>IhKGQC\IFNPT¿J^ NQTCyO ′ CUYRJ9CyNZI TB2@J | JXNQT)NQT)CZY+@VGZJ D| @ D H;NIhr káf M4K+CT ClT+@B@>II\J D NQGQe£NPT k Ì mpo

lY@ Î 4 º 7 3s, 4± f D 3»#9°·3s;#ª35± m CUY@£B2G IU@>H D M4NQC g NZICZY+@ W J9^&^&NQT | k Ì → k CUYRJ9CSC\J9rs@>IJ9Ten^ NPT+CSO k ÌyC CUY@^ NPT+C*O ′ H@>IhB D NPM/@>HJXM t"@ oq ?¶NZI0J g©t"@B2C DÆE @GZH f J/I a @_YJXt@êKRIUKJXGQGQeM/@@TJ/I\IhK W NQT | m [ÜCUY@T=CUY@ Ò NQTB;J D$# W J9^ NZIyJ9GZI B T+CZNQTK KRIhGPexH;N p @ D @TCUNZJ9M4GQ@ olYNZI Ò NQTB;J D$# W J9^ W KRIhCB5J D2D e=CZY+@ D N | NZTRJ9G^ NQTC8^¿C NQC2Ih@G o lYNZInNZI8M/@B;J9KRIh@ f ^ mW KRIhCGQNQ@ T k [JXTHNPCJ9GZI GQNQ@>I T³CUY@B2G IU@>HD M/NQC g CUY D K | Y­^Ö*CUY@wNQTCU@ D Ih@BCUN T gJ9TRH k NZI M/e=J/IIUK W ^&CUN T oi N | K D @né lY@ Ò NQTB;J D$# «J9^

&±F35##z1\ 7 #³:# Î 7 3»,x±Fþ y@ | J D H;GQ@>I\I CUY@BY NQB@>I£NQTt GPt@>HNQTCUY@H;@ E T+NPCUN T f CZY+@^ NQTC^[yCUY@H;NZIhrjI k JXTHk Ì m [FJ9TewC a0¨D @>IUK+GQCZNQT | Ò NQTB;J D$# W J9^AI CUY@ÀI\J W @8BG Ih@>H D M/NQC a NPGQGjM4@nC ^ G | NPB5JXGQGQe

@O/KNQtuJ9GQ@TC f NQT J9BC\[H;N p @ D @TCUNJ9M/GQe@O/KNQtJ4GQ@TC mpolY@ Ò NQTB5J DK# W J9^NZI*N W ^ D C\JXT+CM/@B;J9KRIh@£NQCB T+C2J9NQTRI~J9GQG]CUY@ØNQT pD W J9CZN T J9M KC®CUY@C ^ G | e C D JªÇº@BC D NQ@>IBG IU@³C CUY@³BG IU@>HD M/NQC gyoAfhq T^ D NPT+BNQ^&GQ@>[ | NQt@TCZY+@ Ò NQTB;J D$#W JX^ JbB2G Ih@>H D M4NQC\[ T@®B KGZH D @B TRIhC D KBCjCUY@¤C ^ G | NQB;J9G²IhC D KBCUK D @ C D JªÇº@BC D NQ@>IhT@>J D go¦m çyKCNQCNZIÝIhN W ^&GQ@ D C CUYNQTrJ9M K+CJ W J9^&^&NQT | M4@C a @@T]C a¤ H;NZIhrjICZYJXTJ9GQGsCZYJXCFIh^J | Y@CUCUN oú NPT+B@ YRJ/IyJ E @>H^ NQTCJ9C²^[ a @B;J9TdJ | JXNQTG rJ9CCUY@ µ J9B M/NJ9T W J9C D NQu[»T C JVt@B;C DnE @GZH&[M4K+C CZY+@ W J9^&^>NQT | o lY@ µ J9B M/NZJXT J W J9^>^&NQT |£ NZIFJ | J9NQTH;@ E T@>HJ/IlCUY@IhO4KJ D @ W JXC D NQ ^J D CUNZJXGH;@ D NPtJ9CZNQt@>I\[zNQTCUYNZIB;J/IU@ µ = f ∂ Þ ∂$5 mvo5fhq T D H;@ DpD CUYNZIC W JXru@IU@TIU@>[ a @T+@@>HC ^ D @CU@TRHCUYRJ9C a @YRJ9t"@ | NQt@T pH;N W @TIUN TRJ9G8B D H;NQTRJ9CZ@>IC CUY@nH;NZIhr kno¦m&±F35## 1\ 7 # :# ; ðR;R4 &þ y@ | J D H;GQ@>I\I CZY+@B2Y NQB@ B D H;NQTRJ9CU@>IKRIh@>H vD CZY+@H;NZIhr k [ f a Y+NPB2Y a NQGQGJ p @BCFCZY+@µ JXB M4NZJ9T W J9C D NQ µ m [RCUY@¿ ðR;R4 & CUY@ W J9C D NP µ »a NQGQGAJ9G a J9euI²M/@CUY@£IJ W @ pD J| NQt@TxB2G Ih@>H D M4NQC o TRHI V TB@J | J9NQT a @VB;J9T^&GJ9eCUY@V@N | @TRtuJ9GQK@ | J W @ o TRJ9G | KRIC CUY@zCZ@ D W NQT G | epD IhC\JXCUN TRJ D e^ NQTC\I\[ a @B5JXGQG²JB2G Ih@>H D M/NQCÏ å ±F3¸:*4 7 N CZY+@L@N | @TtuJ9GQK@>I µ GQNQ@n41Z1# Ï z º# 7 º3 7 LNQTCZY+@¤B W ^&GQ@^&GZJ9T@ o I]NQTÓCUY@§B;J/Ih@ Ye"^&@ D M GQNQB`IhC2J9CUN TRJ D e^ NQTC\I\[ Ï å ±F;3¸:*4 77 & 35:² º#9Ó3» 7 4 å #ª35 7 #ª3s å #94:² JI W JXGQG^&@ D CUK D MJ9CZN T CUY@8t"@B2C D0E @GZH8T+@>J D J£Y+e"^&@ D M GQNPB BG IU@>H D M4NQC a NQGQG D @>IUK+GQC NQT JC ^ G | NQB;J9GPGQe£@O/KNQtuJ9GQ@TClt@BC DE @GH o

Page 13: Notes on the Topology of Vector Fields and FLows

¢£ CZ@>I TCUY@¤ ^ G | e ?@B2C D i NQ@GZH&IJXTH i G a I ¥ +

7 4R;3»; å þ¸N JXT+enB2G Ih@>H D M/NQC JXTJ D M/NQC D J D e®t"@BC D¨E @GZHNIG B5JXGQGQe¾IhC D KBCUK D J9GQGPexIhC2J9M/GQ@>[XCUY@TNQC W KRIUClM/@0Ye"^&@ D M GQNQB of ¢£ CZ@Y a CUYNZIHN p @ D I pD2 W Ye"^&@ D M GQNQBNQCUepD IUC\J9CZN TRJ D e^ NQTC\I\[ a Y+@ D @VCUY@³@N | @TtJ9GK@>I CZY+@nJ9^&^ D ^ D NZJ9CZ@ µ JXB M4NZJ9T W J9C D NQ µ ?T@@>HC GQNQ@d1U10# Ï ð+ º43 å )+ o lY@KT+NPC£BN D BGQ@NZI£CUY@N W J | @ CUY@N W J | NQTRJ D eJ9"NZI¤KTRH;@ D CZY+@=B W ^&GP@@"^ T+@TCUNJ9G W J9^A^&NQT | [JXTH¯CZY+NI D @c+@BC\ICUY@@"^ T+@TCUNJ9GD @GZJ9CZN TIUYNQ^ M/@C a @@T t@BC D_E @GZH&I¬J9TRHW JX^&^&NQT | I o¦mÃ*T+B@J | JXNQT[/CZY+@n@N | @TtuJ9GQK@>IJ D @CUY@ D C\I Jd^ GQe"T W NZJ9G NQTÝCZY+NIVB;J/IU@¨CUY@¨^ GQe"T W NJ9GNZIH;@C f µ

λqÉmpo ú NQTB@ µ NZI)J ×

W JXC D NQ[XCUYNZIR^ GQe"T W NZJ9GsNZIÇÈKIUCFJ¤O4KJ4H D JXCUNQB^ GQe"T W NZJ9G[ a NPCUY D @>J9GsB @ pE B2NP@T+C2I oÊ @TB2@CUY@ D C\I¨J D @@NQCUY@ D M CZY D @>JXGZ[ D@GZIU@B W ^&GQ@B T4ÇÈK | J9CZ@>I o*q T­J/H>H;NQCUN TR[CUY@^ D H;KB2C CUY@@N | @TtuJ9GQK@>I W KRIUCM/@^ IUNZCUNPt@>[/IUNQTB2@ KBGQNZH;@>JXT¨Ih^JXB2@¤NZI D NQ@TC\JXM/GQ@ of lYNZI8NZICUY@ ¥ pH;N W @TIUN TRJ9Gt"@ D IUN T CUY@ J9BCCUYRJ9CJ«@QM/NQKRIMJ9TRH=B;J9TT CM/@JIUK+MIh@C CUY@]^&GZJXT+@ oËm ú N M CUY§@N | @T+tuJ9GQK@>IJ D @ D @>J9GZ[lCUY@e W KIUCYRJ9t@¨CZY+@I\J W @IUN | T o@¤B TRIhNH;@ D CUY@¤^ IIUNQM/NQGPNQCUNQ@>I

: å ±F;35: 7 .*+&3¸: #9 % f C © JXTH C ó D @ @ D C CUY@C a¤ @N | @T+tuJ9GZK@>IÖ9CZY+@¤TK W M/@ D NQT | NZI T IUN | TN E B;J9TB2@ m o ç CZY D C\I D @>J9G

J o C © > [ C ó > /S3 7 7 &¨35:² º#

M o C © R [ C ó R / ºS8 7 &¨35:² º#

B o C © > [ C ó R /N m M CZY D C\IR^ IUNQCUNQt"@4þ

luª 7 &435:² º#

NQN m M CUY D2 C2IT@ | JXCUNQt"@ #ªà #9&¨lu 7 +&3¸:² º# ©

o g W ^&GQ@£B TǺK | J9CU@ D2 C2I J o ç CUY K+C2IhNZH;@¤CUY@¤K+TNQClBN D B2GP@

±l 3»*S3 7 7 &¨35:² º#M o ç CUYxNQTIUNZH;@¤CUY@0KTNQClBN D B2GP@

±l 3»* 8 7 &¨35:² # TRH pD B W ^&GP@CU@T@>II[ a @ÆJ9GZI W @TCUN TCUY@ D J9CZY+@ D IUN W ^&GP@dBGZJ/I\IhN E B;J9CUN T Ye^&@ D M GQNPBLB2G Ih@>H D M4NQC\INQT H;N W @TRIhN TI\[ a Y@ D @CUY@ µ JXB M4NZJ9T W J9C D NQLNZI T+GQe × ["J9TRHCUYRJ9CIhNPT | GQ@Ð@GQ@ W @TC¶ ­CUY@ÐG T@>[xT@B2@>I\IJ D NPGQeD @>J9GZ[9@N | @TtJXGQK@ µ h: å ±F;35: 7 .*+&3¸: #9 ¹ o C > /

43 7 7 +>¨35:² # o C R 8

8 7 +&3¸: #&#35 º 7 R Ú ¼ +#ª35 º 7 ùS±F4ð å þ ^ G | enNZI CZ@TB;J9GQGQ@>HK^ TC H;@>IUB D NQM4@=JIhNPCUKRJ9CUN T a Y@ D @ T@êIU^J9B@T NZI­IUNQCUCUNPT |NQTRIhNH;@ fv @ W M/@>H>H;@>H0NQT \m J9T CUY@ D IU^J9B@U o/q TCUYNZI£B;J/Ih@>[J]HNZIhCZNQT+BCUN T¶NI W J/H;@M/@C a @@TR^ D ^&@ D CUNQ@>I¿CUYRJ9CH;@^&@TRH TGQe TV[J9TRHCUY Ih@dCUYRJ9C8B W @¿JXM KC pD W # Ï à¨ å à Ï 7 Ï ] ±F #ª 4&x l olY Ih@8^ D ^&@ D CUNQ@>ILH;@^&@TRH;NQT |³ T+GPe T@`J D @B;J9GQGQ@>Hx º#35 º 7 [lJ9TRHCUY Ih@H;@^&@TRH;NQT | T

WYX[Z)\^]Y_-_`ba4`dce\f]/g3hceikjlgbm * `da4no`qpj-c$p/pr`bsYgdmt`b\a4uMmthv]Ypwmtcexp/]Y_l_ygdmhgbc$prm$_zcesY`dap|~uM`dhuhv]/\M\MceacehhMx+cetp/]Y_l_ygdmpwa]Ya4`dce\f]/njlce`b\Mapa4|~`qpwa4`d\MXuM`qp`qp)_ymea4meha]/sYgdmsYna4uMmpr`bv\cexa4uMmme`bvme\M]/gbMm$p ( |~uM`dhuikfpwasYma4uMmp/]/ikmpw`dv\tsYnt]jlm$v`bcefphceikikme\Ma 2 XuM`qpa4megdgqpfpa4uf]/aa4uMmme`bvme\f_y`dmeha4`dce\fp]/ma]/$me\sYnta4uMmzce`b\Mhv]/ziE]/joa4cza4uMme`bcej-jlc$pw`da4m_y`dmehva4`dce\fp/XuMmce\Mgdn|]/na4uM`qphv]/\sYm]/hhceikjlgb`qpwuMm$_sYna4v]w4meha4c$`dm$p\Mm$]/ ]hgdc$pwm$_3cesY`da`qpsYna4|~`qpwa4`d\MX

Page 14: Notes on the Topology of Vector Fields and FLows

9×8 ¢£ CU@>I TCUY@0 ^ G | e ?A@BC D i NQ@GZH&IJXTH i G a I

CUY@ W JXT+T@ D NQT a YNQBYÓIUNQC\I£NQTRIhNZH;@¯J D @B;J9GQGQ@>Hn+#ª35 7 o¼ #35 º 7 ùS4±Fð å 1.*ª& 6 35:² #9þ o a NZIUCUNQT | H;K@¤C CUY@0@ W M/@>H&H;NQT |uq TCZY+@0B;J/Ih@ J¤BG IU@>H D M/NPC\[ a @ W J9eCUYNQTr ®J/I D @^ D @>IU@T+CZNQT | JnI W JXGQGuT@N | YM D Y H¢ fhgm CZY+@zBG IU@>H D M4NQC g [&J9TRHJ/I D @^ D @>Ih@TCUNPT | KB2GQNH;@>J9T¨IU^J9B@¤ õ o]Y@CUY@ DFD T C g NIJ¤C a NIhCU@>HLBG IU@>H D M/NPC\[CUY@zT@N | Y+M D Y H ¢ fhgym W J9e D W J9e8T CSM4@@ W M4@>H&H;@>HNPT õ a NQCZYC a NZIhCZNQT | H;K+@]I GQ@GPeC CUY@B2Y NQB@ @ W M/@>H&H;NQT | o lY+NI=%#ª3¸ º° 7 C a NZIUCUNQT | B;J9T BB2K D NQTJXT+enNQTCU@ | @ D W K+GCUNP^&GQ@ ¥ ø Á ° C a NZIUC\I o

ç o ;¤T CZCUNQT | TedIUN W ^>GQ@8B2G IU@>HnBK D t"@nNPT õ f a YNQBY¿JXT+eBG Ih@>H D M/NQC W KIUCM/@ m NZISNPT+C D NPTIUNQB;J9GQGQe8C ^ G | NQB;J9GQGQe@O4K+NQtuJ9GQ@TCC JXT+e CZY+@ D IUN W ^&GP@BG Ih@>HBK D t"@>[X^>K D @GQe³J/IyJC ^ G | NQB;J9GIh^JXB2@ oi D W CZY+@@C D NQTRIUNQB^ NQTC tNP@ a [¸Y a @t@ D [CUY@ D @bJ D @ W J9T+e a JXeI=NPT a Y+NPB2Y´JIhN W ^&GQ@BG Ih@>H=BK D t"@³B5JXT]M/@³@ W M4@>H&H;@>H=NQT] õ o a¤IhN W ^&GQ@³BG IU@>H=B2K D t@>I g © J9TRH g ó NQT) õVJ D @B TIUNZH;@ D @>HÔC YRJ9t"@C ^ G | NQB;J9GQGPe­@O/KNQtJ4GQ@TC£@ W M/@>H&H;NPT | IN CZY+@ D @NZIJY W @ W D ^&YNZI W pD2 W õC NPC\Ih@G CZYJXCB5J D2D NQ@>I g © TC g ó o]f &@BY+TNQB;J9GQGQeX[CUY@ IUNQCUKRJ9CZN T NZIIhGPN | YCUGPe W D @]B W ^&GPNQB;J9CU@>HCZYJXT`CZY+NI[SM/KCT Cl@T K | YC M/@ a0D CUY W @TCUN TNQT | oËmlY@ D @>IUKGQCUNQT | @O/K+NPtJXGQ@T+B@ BGZJ/I\Ih@>I J D @B;J9GQGQ@>H8l4#£# å ±F& o lY@rsT CLCZe^&@ruT a TJ/ICUY@n8l4#¤NZICUY@@O/KNQtuJ9GQ@TB@BGZJ/II

CUY@LKTNQCBN D BGQ@LNQTCZY+@0eu·^&GZJ9T@ o TeIhN W ^&GQ@BG Ih@>HBK D t"@NQTVCUY@rsT CCUe"^&@ CUY@K+TrsT C8l#ª#9& olY@8^ D M/GQ@ W B2GJ/IIUN e"NQT | rsT C\IyNZIzJ£t@ D eH;N pE BK+GPC T@>Ö W KBY ^ D2|"D @>II´YRJ/IáM/@@TW J4H;@>[M/KC W K+BY D @ W J9NQTRIC M/@~KTRH;@ D IhC H o IJ9TÔ@uJ W ^&GP@ CUY@H;N pE B2KGQCZe CUY@ÝIUKM9Ǻ@BC\[ a @B2NQCZ@ T@ D @>IhKGQCxCUYRJ9C a J/IB T4ÇÈ@BCUK D @>H pD J¶G T | CZN W @>[M/KCd^ D2 t"@>H TGQexJB K+^>GQ@ e"@>J D IJ |">ù Ï &3»;þ a0 IhN W ^&GQ@£BG IU@>HBK D t"@>INPT õ0J D @ CZY+@³I\J W @LruT CCUe^>@zN J9TRH TGQe8N CUY@N D B W ^&GQ@ W @T+C2J D e D @ | N TI¿NQTÑ õ­J D @C ^&G | NQB;J9GPGQe£@O/KNQtuJ9GQ@TCFIh^JXB2@>I o Te"CUYNQT | CZYJXCJIUN W ^&GP@BG Ih@>HBK D t"@B;J9TH NQT= õX[4JBG IU@>H D M4NQC Jt"@B2C DE @GZH¤B;J9T^ CU@TCUNJ9GQGQeH J/I a @GPG o ú J9T+ersT CVCUe^>@B;J9T BB2K D J/IlCUY@¤rsT ClCZe^&@ JBG IU@>H D M/NQCNQTI W @¤t@BC DyE @GZH ogyo ãlNQTrsNQT | Te8B GQGQ@BCUN T C a0LD W D @VH;NZIpÇ NQTCIhN W ^&GQ@B2G IU@>HBK D t"@>IzNQT¿ õ W J9ed@"Y+NQM4NQCzGPNQTrlNQT | [sJ9T CUY@ D @C D NQTRIUNQB^ D2 ^&@ D CUe o ãlNQTrsNQT | NZID @>J9GQGQeǺKRIhCCZY+@ | @T+@ D J9GPNZXJ9CZN T rsT CUCUNQT |J9^&^ D2 ^ D NZJXCU@¾C J E T+NPCU@­K+TN T IhN W ^&GQ@BG Ih@>H0BK D t"@>I o TRJ9G | KRIzC rsT CZCUNQT | [ a @H;@ E T+@CUY@B GGQ@BCUN T g © [ o¦oËo [ g H;NZIvÇ NPT+CyIhN W ^>GQ@¤B2G Ih@>HBK D t"@>I)NQT õC M/@Ô 8 &½&S ºR4;#wC J9T CUY@ D IhKBY=B GPGQ@BCUN T k © [ oËoËo [ k N CUY@ D @NZIJ)Y W @ W D ^&YNZI W õC NQC2Ih@G CUYRJ9CB;J DD NP@>ICUY@¾KTN T g © ∪ oËo¦o ∪ g TC CUY@KT+N T k © ∪ oËo¦o ∪ ksouf lYNZILN W ^&GQNQ@>ILCZYJXC\[uNQT J9BC\[5@>J9BY g ¸NZI*B;J DD NQ@>H TC T@ CUY@ k 5 oËm I a NQCZYwrsT CZCUNQT | [jJ9Tw@O/KNQtuJ9GQ@TB@BGZJ/I\I GQNQTrjIRNZIRB;J9GQGP@>HVJ 8¨# å ±F o

Page 15: Notes on the Topology of Vector Fields and FLows

¢£ CZ@>I TCUY@¤ ^ G | e ?@B2C D i NQ@GZH&IJXTH i G a I é +

TedB GQGP@B2CZN T BG IU@>H D M4NQC\I Jt"@BC DE @GZH NZI_JÑB GPGQ@B2CZN T H;NIpÇ NPT+CÓIhN W ^&GQ@BG Ih@>HBK D t"@>INQT~ õ9[LJ9TRH`J4I]IhKB2Y D @^ D @>Ih@TC\I¶JGQNQTrCZe^&@ o «KBYÓNZI)ruT a T[LM/KCW KBY D @ W J9NPTIKTrsT a TR[J9M KC a YJXCGQNQTrCUe"^&@>I§B;J9T B TIUCUNQCZK+CZ@ÓCUY@ Ih@C I K D B@BG Ih@>H D M/NQC2I[IJ/H&HGQ@ÐBG IU@>H D M4NQC\I\[dJ9TRHIhNPT+rBG IU@>H D M/NQC2I Jt"@B2C DzE @GHH;@ E T+@>H T õ D J8IUK+M+Ih@C õ o IÀJ9T®@uJ W ^&GP@ CUY@NQTC D N | K+NPT | IhC2J9CU@ N | T D J9TB@ CUYNZIIUNQCUKRJ9CZN T[ a @ W @TCUN T®J J W KIKTI GQt"@>H¶^ D M/GQ@ W rsT a T_J/ICUY@ú @N @ D CB TǺ@BCUK D @>[^ IU@>H t@ D×Á e@>J D IJ |">ù Ï ' ; º1\;35# 7 +ñX 7 #ª3s>þú K^&^ IU@?¾NZIVJxT TpIUNQT | KGZJ D I W CUY f N o @ o [g ∞ m t"@BC DE @GH®H;@ E T+@>H TÐJI GPNZHC D KRIf J9TBY D0D NPT | m IUYRJ9^&@>H D @ | N T ú NQT ¥ o/i K D CUY@ D IhK^&^ Ih@bCZYJ9C? NZI^ NPT+CZNQT | NQT a J D HT D W J9G TCUY@¤C D KRIRM KTH&J D e ú o K+@>IUCUN T «dKRIhC? T+@B@>II\J D NQGQe­YJXt@áJ9TeBG Ih@>H D M/NQC2IJ9CFJ9GQG7lY@ ED IhCn@uJ W ^&GQ@>I IUK+BY~Jt@BC DE @GHCUYRJ9C T@B W @>IK+^ a NQCUYáKRIhKRJ9GQGPeYRJ9t"@`JBG Ih@>H D M4NQCCUYRJ9C | @>I=J D K+TRHCZY+@Y GQ@NQTCUY@I GPNZHC D KRI ú o ú K D ^ D NZIhNQT | GQeÆ@T K | YR[CUY@ D @VJ D @0@uJ W ^&GQ@>I g ∞ t"@BC DFE @GZH&II\J9C2NZI eNQT | CZY+@b^ D @ W NZIU@>I ú @N @ D C Å I g TǺ@B;CUK D @>[yM/KC a Y Ih@BG Ih@>H D M/NQC2I)H # |"J D KTHCZY+@¾Y GQ@¾NQT ú oq T J/H>H;NQCUN TR[CUY@J9TRI a @ D NZIjrsT a T=C M/@ J9GZIU@N CZY+@H;N p @ D @TRCUNJ9M/NQGQNPCUexB TH;NPCUN T¨NZI D @GZJ9"@>HVC n T+GQe g© Dg ó oll;u q T¶GZJ9CU@ 66 ¥ CZY+@ g ∞ ú @N @ D CB T4ÇÈ@BCUK D @ a J4I p KTRH~C M/@ J9GZIh@ a Y@T; D euIhCZeTRJ;¤K+^&@ D M/@ D|¾ K+M4K D T¯T+NQt"@ D IhNPCUe®J9TT KTB2@>HJB KT+CZ@ D @uJ W ^&GQ@>[ a YNQBYJ/I «J D B2Y 66 × J9^&^&@>J D IRB DD @BC o

< ß ' #9:²Ob º1\ªlq Ê D @^ D @>Ih@TC\IbJYe^&@ D M GPNQB`IUC\J9CZN TJ D e^ NQTC D B2G IU@>H D M/NQC Jt@BC DyE @GZH&[9CZY+@ D @J D @LN W ^ D C\JXT+CC ^ G | NQB;J9G @>J9CUK D @>ISGQK D ruNPT |T@>J D M/e CUY@I ·B;J9GPGQ@>H)IhC\JXM/GQ@J9TRHÀKTIUC\J9M4GQ@W JXT+N v GZH&I Êoi D B Tt@TNQ@TB@ a @ W J9rs@¤CUY@; #ª þ ~7 35 º# 7 0;ª;# Jt"@B;C DE @GH?]NZIyJ9Te³IUC\J9CZN TRJ D ez^ NQTC D BG IU@>HD M/NQC ? olY@³IUC\J9M4GQ@ W J9TN p GZHzNZISCZY+@VIh@C J9GQG^ NPT+C2Ic a NPT | NQTC Ê NQT^ IUNQCUNQt"@CUN W @>Ö¸CZY+@KTRIhC2J/M/GQ@ W J9TN p GZH¤NZIRCZY+@8Ih@C J9GQGs^ NQT+C2IRc a NQT |NQTC Ê NQTT@ | JXCUNQt"@0CZN W @ oà ^J D CUNQBKGZJ D NQTCU@ D @>IUCNZIY a CZY+@`IUC\J9M4GQ@W JXT+N v GZH T@B D NQCUNQB;J9G+@GQ@ W @TCSNQTCU@ D Ih@BC\ICUY@0KTRIhC2J9M/GQ@ W J9TN p GZH J9T CZY+@ D [ D ^ IIhNM/GQe NQC\IU@G o;fhq C a NQGQGM4@zGP@ CC CUY@ D @>J4H;@ D C KTH;@ D IUC\J9TRH a Y+e£C a¤ H;N p @ D @TCIhC2J9M/GQ@ W J9TRN p GZH>IRB5JXT+T ClNQTCU@ D Ih@BCl@>J9BY CZY+@ D oËm

' #9:²Ð º1\ªl´41 Ï å ±F3¸: 7 #9°#ª 3 å ±F4 º#9þ@VT a B TRIhNZH;@ D J9T CUY@ D N W ^ D C2J9TCC ^ G | NQB;J9G @>J9CZK D @>I J9Te)Ye^>@ D M GQNQBxB D NQCUNPB5JXG@GQ@ W @T+C CUY@IhC\JXM/GQ@J9TRHÝK+TRIUC\J9M/GP@ W J9TNZp GZH&I o IIUK W @ÔCUY@ D @ÔNZI¶Jt"@B2C DE @GZH§?H;@ E T+@>H TI W @ ^&@T¨IU@Cl§NQT ó D õ o; #ª þ ãl@CÀ^`M4@§JYe^&@ D M GPNQBIUC\J/CUN TJ D ez^ NPT+C CZY+@t@BC DE @GH¤? o lY@#9°:²x 124 CZY+@³^ NPT+C ^[ÓH@T CZ@>HM/e8 ë f ^ m [;NZICZY+@³IU@C ^ NQTC\I a Y Ih@zC D JǺ@B;C D NQ@>IyJ9^&^ D J9BYx^J/IlC → ∞ o lY+@#9:² º1\ª CUY@ ^ NQTC´^[H;@T CU@>H M/e

Page 16: Notes on the Topology of Vector Fields and FLows

ø ¢£ CU@>I TCUY@0 ^ G | e ?A@BC D i NQ@GZH&IJXTH i G a I

¡ f ^ m [¸NZI0H;@ E T@>HJ/I*CUY@xIhC2J9M/GQ@ W J9TN p GZH ^ pD CZY+@ D @t"@ D Ih@>H8c a o"fhq T CZY+@ Da¤D H&I["NQCNZIÀCZY+@IU@C ^ NQTC\IÀ a Y IU@¿C D JǺ@BC D NQ@>IJ9^&^ D2 JXB2Yx^J4IRC → −∞ oËmq TdJ9GPG»B;J/Ih@>IjCUY@8IUC\J9M4GQ@ W JXT+N p GZH JYe^&@ D M GQNPB IhC2J9CUN TRJ D e ^ NQTC NZI C ^ G | NQB;J9GQGQe@O/KNQtuJ9GQ@TCjC J KB2GPNZH;@>J9TdIh^JXB2@ o lYNZIlB ^&e NZI W J9^&^&@>HwNPT+C CUY@®H W JXNQT CUY@t"@B2C DE @GZH g©f J/IlG T | J4Il?wNI m J9TRH T@>·C T@ o& ¹ u ; ;[J I K D B2@^nYRJ/I J Á H;N W @TIUN TRJ9G8IUC\J9M/GP@ W J9TN p GZH CZY+@^ NPT+C8^NQC2Ih@G oq ^NZIJÑI\J/H&H;GQ@>[xCUY@T ^YRJ/I J pH;N W @TRIhN TRJ9G¤IUC\JXM/GQ@ W JXT+N p GZH&[uB TRIhNIhCUNPT | ^JXTHCUY@C a0£D M/NQC\I0JXG T | CUY@T@ | JXCUNQt"@@N | @THN D @BCZN T o4q ^­NZIwJ§IUNQTrl[CUY@`IhC\JXM/GQ@W JXT+N v GZHÝNZI pH;N W @TIUN TRJ9GZ[B TIUNZIhCZNQT | JXCGQ@>J/IUC J9GQGCZY+@=^ NQTC\IIUK pE BNQ@TCUGQeBG Ih@=C ^[jJ9TRH¨J9GPGCUY@x^ NQTC\I¤CUYRJ9C@t@TCUKRJ9GQGPec aNQTC CUY@ W o& % u ; ;[8J I K D B@®^ YRJ/I JÁ pH;N W @TRIhN TRJ9GzIhC\JXM/GQ@ W J9TN p GZH o IJ/H&H;GP@ CUe"^&@ f KC\[ NQT m YRJ/IJ pH;N W @TRIhN TJXGIhC2J9M/GP@ W JXT+N p GZH J | J9NPT¨NQC a NQGQGjM/@nCUY@n^ NQTC^­JXTHCUY@^ D @BNZIh@GPewC a0¨D M/NQC\IJ9G T | CZY+@T@ | JXCUNQt"@³@N | @TH;N D @BCUN T o IJ/H&HGQ@ CUe"^&@f KC\[ NQT m YRJ/IJ pHN W @TRIhN TRJ9GxIUC\J9M/GP@W JXT+N v GZH f N o @ o [9NQClNZIJ8IUK D J9B@ m [9B TRIhNZIUCUNQT |£CUY@n^ NQTCy^]J9TRHCUY@nC D JǺ@BC D NQ@>I a YNQBY | @CJ D M/NQC D J D NQGQeBG IU@xC CUY@xT@ | J9CZNQt"@ D @>J9GS^J D C@N | @T+^>GZJ9T@J/IC → ∞ oÜi NQTRJ9GQGPe9[J£IUNQTrV^8YRJ/IJ ¥ pH;N W @TRIhN TRJ9GjIhC2J9M/GP@ W JXT+N p GZH olY@CZ@ D W °· 124¿NPTC ^ G | e W @>J9TRIJ¨Ih^AJ9B@@>J9BY¿^ NPT+C Fa Y+NPB2YYRJ/I³JT@N | YRM D Y H£CUYRJ9CSNZIC ^ G | NQB;J9GPGQen@O/KNQtJXGQ@TCC J9T ^&@TT@N | YM D Y H³NQT KB2GPNZH;@>J9TIh^AJ9B@ ¡ o»q TM D NQ@ [jJ W J9TN p GZHxNZI8JIh^JXB2@=CZYJXCNZI G B5JXGQGQe KBGQNZH;@>JXT J E @>HH;N W @TIUN TT o

^ NQTC=NIJ Á W J9TN p GZH o BK D t@)NZIdJ W JXT+N v GZH o IhK D J9B@LNIJ W J9TN p GZH o TRH³J¥ W J9TN p GZH&[AN NQC£NZIxJ)IhKMIU@C õ9[ANZIxJ9Te ^&@T¨IUKMIh@C õ o ICUY@~CZ@ D W NQT G | eÐN W ^&GQNQ@>I\[JXT+eÑIUC\J9M4GQ@W JXT+N v GZHÐNZI[³NQT J9BC\[J9T T W J9TN p GZH pDI W @T o lY@TbNQT®O/K@>IhCZN TR[yJ/InCUY@J9M t"@@uJ W ^&GQ@>I¤IUK |"| @>IhC\[¸NZI*CZY+@T+K W M4@ D @N | @TtuJ9GQK@>IRYJXtNPT | T@ | J9CUNQt"@ D @>JXGu^AJ D C oq C p GQG a I pD W CUY@H;@ E TNQCZN TCUYRJ9C=b#9°:²¨3À#9:² 124] £ ºR435 4#l;3# Ï w 7 #ª 1# Ï dâà oAi D CUYNZID @>J/I T CUY@e J D @ I W @CZN W @>I¾B GQGQ@BCUNPt@GQeB;J9GQGQ@>H NQTtuJ D NZJ9TC W J9TN p GZH&I oÊ a @t"@ D [IhNPT+B@0CZY+@ D @J D @ W J9T+e CUY@ D W JXT+N p GZH&ICZYJXCJ D @NPT+tuJ D NZJ9TCK+TRH;@ D CUY@c a [ a @^ D @ @ D T CC KRIh@¤CUYNZIRCU@ D W NPT G | e o

' #9:²£ 124l1 Ï å ±F;3¸:*4 7³7 &3¸: #9þ; #ª þ ãl@C g M/@ J Y+e"^&@ D M GQNPBBG Ih@>H D M/NQC CUY@Vt"@BC DzE @GZH³? o lY@#9°:² 1\ g [ÑH;@T CU@>HÀM4ed ë fhgym [NZIÀCZY+@IU@C ^ NQTC\IÀ a Y IU@¿C D JǺ@BC D NQ@>IJ9^&^ D2 JXB2Y g J/IC → ∞ ofpÊ @ D @®CUY@ a¤D H JX^&^ D J9BY NQTHNQB;J9CU@>I=IhN W ^&GQe¨CZYJXCCUY@]H;NZI\C\JXT+B@ φ è f m C g | @C\IyJ D M/NQC D J D NQGPe=I W J9GPG²J/IC | @C\I£GZJ D| @ o¦m lY@À#:²d4 º1\ g [/H;@T CU@>H0M/e£¡ fhgym [9NIH;@ E T@>HVJ/IRCUY@IUC\J/M/GQ@ W J9TN p GZH g pD CUY@ D @t"@ D Ih@>Hzc a ofhq T CUY@ DFa0D H&I\[;NPCNZICUY@VIh@C ^ NQTC\IS a Y IU@C D JªÇÈ@BC D NQ@>IJ9^&^ D J9BY g J4IRC → −∞ oËmlY@xIUC\J9M/GP@ W JXT+N p GZH JzY+e"^&@ D M GQNQBBG IU@>HD M/NQCNZI8C ^ G | NQB;J9GQGPe)@O/KNQtJXGQ@T+CC @NQCUY@ DCUY@ D H;NQTRJ D e D C a NZIUCU@>H8^ D H;KBC CUY@BN D BGQ@ÝJXTHÝJ KB2GPNZH;@>J9TØIU^J9B@ o¤q CUY@ÝIhC2J9M/GP@W JXT+N v GZH­NZI pH;N W @TIUN TRJ9GZ[ pD @uJ W ^&GQ@>[

Page 17: Notes on the Topology of Vector Fields and FLows

¢£ CZ@>I TCUY@¤ ^ G | e ?@B2C D i NQ@GZH&IJXTH i G a I +

CUY@>Ih@ØJ D @¾CZY+@­B2e"GQNQTRH;@ D JXTH¾CUY@¾«@QM/NPKIMJXTH&[ D @>Ih^&@BCUNQt"@GQe o I*NQTCZY+@£B;J/IU@ J=IUC\J4CUN TJ D e)^ NQTC\[²CZY+@>IU@IUC\J9M4GQ@ W JXT+N p GZH&IJ D @J9GZI W JX^&^&@>H g© J9TRH T@>·C T@wNQTC CUY@H W JXNQT CUY@¤t@BC DE @GZH o& % u ; ;[JI K D B2@8BG IU@>H D M4NQC gYRJ/InJ pH;N W @TIUN TRJ9GIhC2J9M/GQ@ W J9TN p GZH ǺKRIhCNQC2Ih@G o I\J/H&H;GP@¤BG Ih@>H D M/NPClYRJ/IFJ pH;N W @TRIhN TJXGIhC2J9M/GQ@ W J9TN p GZH o IUNQTrÀB2G IU@>H D M/NQCYRJ/IJ ¥ pH;N W @TRIhN TRJ9GjIhC2J9M/GP@ W J9T+N p GZH oú C2J9M/GQ@ W JXT+N p GZH&I8CUYRJ9CJ D @ Dx pH;N W @TRIhN TJXG=G r´GQNPru@ D H;NPTJ D e§BK D t"@>I D IhK D J9B@>I[ D @>IU^&@B2CZNQt"@GQe9[T@>J D CZY+@N D J4II B2NJ9CU@>HBG Ih@>H D M/NQC D IhC2J9CUN TJ D eÀ^ NQT+C o»Ê a @t@ D [J/ILCUY@e | @C J D CUY@ D J a J9eCUY@e | @C a0 KTRHK^NQTbCZY+@wH;e"TRJ W NQB;I CZY+@ D ^J D C\I CZY+@t"@B2C DLE @GZH&[IhKBYJ/I CZY+@ D B2G Ih@>H D M4NQC\I DIhC2J9CUN TJ D ex^ NQTC\I o lYNZIB;J9T¨B;J9KRIh@CUY@ W C M/@¤BK D GQe£M4@e TRH0M/@GQNQ@ o

< ý ùj3»4R;3»4 º# åú K^&^ IU@=CUYRJ9C8J³GQNQT@=GQNQ@>I¤NQTbJ³^&GZJXT+@=NQT] õ o TJ D M/NQC D J D NPGQe¾I W J9GQG^>@ D CZK D MJXCUN T CUY@GQNQT@ D CZY+@8^&GJ9T@ D M CZYB;J9T f J9TRHnKIUKJXGQGQea NQGQG m BYJXT | @ÀCZY+NI³IhNQCZKJXCUN T J CZ@ D CUY@^&@ D CUK D MJ9CZN T[CUY@GQNQT@ a NPGQGJ9G W IhCB@ D C\J9NQTGQeNQTCU@ D Ih@BClCUY@¤^&GZJ9T@¤NQT T@0^ NQT+C o¢£a IhK^&^ Ih@NQTRIhCZ@>J/HCUYRJ9CJGQNPT+@NQTCU@ D Ih@BC\IJ^&GJ9T@¨NQTwǺKRIhC T+@¨^ NPT+C oq TÝCUYNZIB;J/Ih@JIhK pE BNQ@T+CZGQe]I W J9GPGS^&@ D CZK D MJXCUN T CUY@=GQNQT@J9TRH;Þ D ^>GZJ9T@ 7 #bJXGQCU@ D CUYNZI¿IUC\J9CZ@ J p JXN D I oú K^&^ IU@ÆC a¤ W J9TN p GZH&Ib« © J9TRHЫ ó NQT KBGQNZH;@>JXTIh^JXB2@ ¡LNQT+CZ@ D IU@BC0J9C0J£^ NQTC^ oãl@C`SwH;@T CU@_CUY@ IU@C J9GPG t"@B2C D IC\JXT | @TC)C «¢sJXCS^[ pD N = [ o ïà ±F°

±FÔ# Ï #Ý;R;3 å 7 #943Ô Õ ¡ # Ï 41 7 #943 º® © 4R 7 #3 º ó o lY+@T« © JXTH0« ó J D @I\J9NZH0C º#9;3s 7 ##ª3»4R;3»; å 4#*# Ï z±F #^ oq *pD ;R;3 å ^ NQTC^NPT« © ∩ « ó [sNPCNZICUY@B;J/Ih@¯CUYRJ9C§« © J9TRH_« ó NQT+CZ@ D IU@BC§C D J9TRI\t"@ D IU@GQe³JXC²^[ÜCUY@T=« © J9TRH« ó J D @IJXNZH8IhN W ^&GQexC #9;3» 7 #0#ª3sR;3s; å/Ú ¢£ CU@CUYRJ9CN « © ∩ « ó NZIR@ W ^&CZe9[9CZY+@Tx« © JXTH0« ó T@B;@>II\J D NQGQe£NPT+CZ@ D IU@BClC D J9TRIht"@ D IU@GQe o]Y@TxC a¤ W JXT+N p GZH&I H;N W @TIUN TRIH J9TRHH NQT+CZ@ D IU@BCÐC D J9TRIUt@ D Ih@GQe NQT ¡"[]CUY@N DNQTCU@ D Ih@BCUN T ¢ NI J | J9NQTÑJ W J9TN p GZH o­q H Í H R T[9CUY@TNQT J9BC ¢ W KRIUCRM/@0@ W ^&CUe oÃ*CUY@ D2a NZIU@>[ ¢¾a NQGPGM/@=J W J9TN p GZH HN W @TRIhN T@O/KRJ9GsC H Í H T oB Ï ;~#ªà¨wS º1\l º#9;3» 7 #=#3»°R;3»; å -u# Ï ;~w1Z 7 ;#ª å ÈF±F;3»°#ª3¸:*4#ª 4 1Ô& 7 Ï 1¿# Ï à ºÈ)4#7 Ï ð # Ï 1\ 7 # Ú ãlNPru@ Ye^&@ D M GQNPB2NPCUe9[C D J9TRIht"@ D IJ9GPNQCUeNIJ¤^ D ^&@ D CUe a Y+NPB2Y a NPGQGuT CM/@ a J4IhY@>HJ a JXeM/eI W J9GQG@ D2DD I W @>J/IhK D @ W @TC o TRHJ/INQTCUY@VB;J/IU@ Ye"^&@ D M GQNQBNQCUeX[>N C a¤W JXT+N v GZH&IÝH T C]NQT+CZ@ D IU@BCC D J9TRIht"@ D Ih@GQeX[CUY@T¶CZY+@eB;J9TM/@ W J/H;@C H I J CZ@ D J9TJ D M/NQC D J D NQGQexI W J9GQGs^&@ D CUK D MJ9CZN T o< ù Ï Lï° B l;35 ºð ' ;#i D J9TÕJ D M4NQC D J D e`t"@BC DE @GZHÝ?²[ a @®B;J9TH;@ E T+@³CZY+@Ih@C ^ NPT+C2ICUYRJ9C D @BN D B2KGZJXCU@>[ NQTJnIU@TRIh@¤CUYRJ9ClB;J9TM/@ W J4H;@0^ D @BNZIU@ o; #ª þ+@)I\J9edCZYJXC³J^ NPT+CLNZI0ਰl;35 ðN @t"@ D eT+@N | YM D Y H CZY+@¤^ NPT+C2[J CZ@ D c a NQT | pD J IhK pE B2NQ@TCUGPe GJ D| @J W K+TC CUN W @>[=T+@t"@ D NQTCU@ D Ih@BC\I®NQC\IU@G J | J9NQT o

Page 18: Notes on the Topology of Vector Fields and FLows

! ¢£ CU@>I TCUY@0 ^ G | e ?A@BC D i NQ@GZH&IJXTH i G a I

Ò D @B2NIh@GQe ^`NZI a J9TRH;@ D NQT | ^ NPT+C pD ?N CUY@ D @0@"NZIUC\IJT@N | YM D Y H ¢§ ^J9TRHJ > Á IUK+BYCUYRJ9C\[ pD JXGQGAC a NQCUY |C | ≥ [ a @YRJ9t"@ φ è f ¢ m ∩ ¢ = ∅.; #ª þ~lY@ °·à¨l3¸ ºð ;#Ωf ? m JÝt@BC D¿E @GH§? B TRIhNZIUC\I J9GQG^ NQTC\IRCZYJXCFJ D @0T C a J9TRH;@ D NPT | où Ï Õ°·à¨l;3¸ ºð ;#Ш#Ð:* 7 &;#0 ºSR3¸ S#0l;3=# Ï 7 #ª 1R# Ï Lâ4à Ú å7 35 º#ª 7 4;;;#x41R 7 #93; 7 &35 å 7 4#9 & º#9°à¨l;35 ð;# Ú uJ W ^&GQ@ i D J9Te D > Á B TIUNZH;@ D CUY@³B TRIhC2J9TClt@BC DE @GHL?S£ TCUY@¤K+TNQCFIUO/KRJ D @Á ≤ ≤ π [ Á ≤e ≤ π [ | NQt"@T¨M/ex?£ f [/e m ≡f [ D ó mposq a @£NH;@T+CZN e ^&^ IUNQCU@=IhNH;@>I CZY+NIIhO4KJ D @0tNJ f u[ Á m¤f [ π m JXTH f Á [e m¤8f π [e m [a @ | @CJC D KRI a NQCUY´Jt"@B2C DE @GZH TÔNQC oi NQTRJ9GQGPe a @B;J9T E GQG&K+^J£I GQNHnJXT+BY D*D NQT | NQT õFM4eT@>IhCZNQT | JXTNQT E TNQCU@ J W NQGPe IhKBYC D N D @t GQKCUN T T@ pD @>J9BY D I\J9CUNZI eNQT |bÁ¦¥D§¥® / J9M KCJB D @dB2N D BGQ@ o @NQTRIhB D NQM/@8CZY+@8t"@B2C D0E @GZHn?S£ TCZY+@8C D KRI I W J9GQG D J4H;NQKRI D o lY@T­CUY@wT T a J9TRH;@ D NQT |Ih@C CUYNZIRt"@BC DyE @GZH T NZIFJ9GQG où Ï &3»;þ ú K^&^ Ih@nCUY@t"@B2C DLE @GZH?ÝNZIR4 &° ±R3»&;35 ð 4 :*4l&l )ØJ9TRHzYRJ/In#3»ÜñX 7 #93¸ &z% #9° ºSð º#9Ll Ú lY+@T Ωf ? m W KRIhClM/@nJ9GQG o' 8F;# 7 Ï 1)±l3»+1\þ ú K+^&^ IU@>[0C CUY@ÝB TC D J D e9[/CZYJXCFCUY@ D @nNZII W @n^ NQTCF^ ¬J9TRHI W @T+@N | YM D Y H ¢Ô ^ÀIUK+BY=CUYRJ9C pD J9GQG|C | ≥ > Á [ a @¤YJXt@ ¢ ∩ φ è f ¢ m = ∅ o¢£a [;N CUY@ D @ a @ D @zC a¤ TK W M/@ D II J9TRH=I

a NQCUY¨I 2 ≥ I Í A[/IhKBYCUYRJ9Cφ ë © f ¢ m ∩ φ ë ó f ¢ m ≠ ∅ [XCUY@TM/e=J9^&^&GQe"NQT |φ− ë © C M CUYØIhNH;@>I CZY+NI@"^ D @>IIUN T a @a¤ K+GH M4C\J9NQT ¢ ∩ φ ë ó − ë © f ¢ m ≠ ∅B T+C D J4H;NQBCUN T olYKI a Y@T+@t"@ D CzNQTB D @>J/Ih@>IM4e¿J9CzGQ@>J4IhCzA[φ è f ¢ m W KIUC BB2K^&eJT+@ a§D @ | N T a NPCUY@O/KRJ9Gn^ IhNPCUNQt"@t GQK W @>[ a Y+NPB2Yá@t"@TCUKRJ9GQGQea NQGQG²@YRJ9KRIhCyCUY@nT@B@>II\J D NQGQe E TNQCZ@nt GQK W @ B TC D J/H;NQBCUN T o

< ' #ª35 7 #ªS3» ' #9:² º# åq £a @bJ D @@t"@ D|" NQT | C M4@bJ9M/GQ@]C JXB2BKRD J9CU@GPe H@>IhB D NPM/@CZY+@ØC ^ G | e J D @>JXGZa¤D GH¾t@BC DbE @GH&[CUY@TêCUY@­T+@B@>II\J D NQGQeNQTRJ9BBK D J9CZ@¿TK W @ D NQB5JXGH@ E TNQCUN T a @¿YRJ9t"@ CUY@át"@BC DÔE @GZH W KRIhCT C§J p @BCCUY@C ^ G | e o @J D @nCUYKRINQTCU@ D @>IhCU@>HNQTt@BC DE @GZH&I a Y+NQBY rs@@^êCUY@N D§| G MJ9G¨C ^ G | e@t"@TJ CZ@ D J®IUK pE BNQ@TCUGQe­I W J9GPG£^&@ D CZK D MJ4CUN T olYNZI²NZI²@JXB2CZGQeLCUY@B TRIhNZH;@ D J9CZN T a Y+NPB2Y³GP@>HC n K D0| NQt"NQT | ^ D W NQT@TB2@nC Ye"^&@ D M GQNQBNQCUeX[J9TRHC D J9TRIht"@ D I\J9GQNQCZe9[u@"B@^&C¤CUYNZI0NZI0T C*ǺKRIhC T¨JG B;J9GjIUB5JXGQ@ NQClNI T¨J | G MJ9GjIhB;J9GP@ o; #ª þ t@BC DFE @GZHz? TÀ`NZISB;J9GQGP@>H#ª35 7 #ªS3» å #9:²£N pD J9TenT@ a t@BC DE @GZH? © T~CZYJ9CNZI¤IUK pE BNQ@TCUGQeT@>J D C ?f NQT`CZY+@ g© IU@TIU@ m [CUY@ D @@"NZIhC2I¨J)Y W @ W D ^&YNZI W Ê → a YNQB2YÝB;J DD NQ@>ICUY@C D JªÇÈ@BC D NQ@>I ?¯C CUY Ih@ ? © J9TRH)^ D @>Ih@ D t"@>IRCUY@N D IU@TIU@ oq TM D NQ@ [»J³I W J9GQG+@T K | Y^&@ D CUK D MJ9CZN T ?D @>IhKGQC\I0NQTÝJxT@ a t@BC D8E @GZHCZYJXC0NZI0C ^ G | NQB;J9GQGQe@O/KNQtJXGQ@T+ClC CZY+@ GZH T@ o¢£ CZ@ q C W N | Y+CM/@T+NPB2@C M4@wJXM/GQ@C I\J9eCUYRJ9CCUY@ GZHJ9TRH¿T@ a t@BC DE @GZH&I a @ D @

Page 19: Notes on the Topology of Vector Fields and FLows

¢£ CZ@>I TCUY@¤ ^ G | e ?@B2C D i NQ@GZH&IJXTH i G a I 6 +

I W CUYGQe @O/KNQtuJ9GQ@TC f N o @ o [ÔC ^ G | NQB;J9GQGQe@O/KNQtuJ9GQ@TCnt"NZJJY W @ W D ^&Y+NI W CZYJXCnNZII W CUY J9TH­YRJ/IÝI W CZYêNQTt@ D IU@ mpo£Ê a @t"@ D [uI W CZYd@O/KNQtuJ9GQ@TB@^ D @>IU@ D t@>Iy@N | @TRtuJ9GQK@>I J9C IhC\JXCUN TRJ D e ^ NQT+C2I[ M/KC@N | @T+tuJ9GQK@>IxB;J9T§M/@]@>J/IUNQGQeBYRJ9T | @>Ht"NZJ¶Jg© ^>@ D CZK D MJXCUN T o¼ R4¨±lª>þ g TRIhNZH;@ D CUY@]B TRIUC\J9TC=t"@B2C DE @GZH? f u[e m = f J/[M m TV ó o lY+NI²NZIIhC D KBCUK D J9GQGPexIhC2J9M/GQ@>[4J/IRe K W N | YC | K@>II o¼ R4¨±lª>þ g TRIhNZH;@ D CZY+@ t@BC D E @GZH| NQt@TxM/e? f u[e m = f −e Í f &ó Í e&ó − m [9 Í e f &ó Í e»ó − mpmpolYNZInt"@B2C DE @GZHYRJ/I T@IhNPT+r`IhC2J9CUN TRJ D e^ NQTC\[AJ9TRH T@I K D B@VBG Ih@>H D M/NPC oAq C\[>C [NZIIUC D K+BCUK D J9GQGPexIhC2J9M/GQ@ o< $ Ob3»&° ' zy 7 #93y ;l« D IU@> ú W J9GQ@wt"@BC DdE @GZH&I¨J D @wN W ^ D C2J9T+CM/@B;J9KRIh@xCUY@ewJ D @CZY+@IhN W ^>GQ@>IhC¤GZJ D| @xB2GJ/II IhC D KBCUK D JXGQGQexIUC\J9M/GP@0t"@BC DyE @GZH&I o; #ª þ t@BC D´E @GHê? NZI`B5JXGQGQ@>HOb3»&° ' LN CUY@ p GPG a NPT | Y GZH m ?ØYRJ/IÀJ E TNQCU@TK W M/@ D IUC\J9CZN TJ D e^ NQTC\I=J9TRHB2G IU@>H D M/NPC\I[SJXGQG a YNQBY§J D @Ye^&@ D M GPNQB o m lY+@T T a J9TRH;@ D NQT | Ih@C Ωf ? m NIÀCUY@KT+N T CZY+@BG IU@>H D M/NQC\I0J9TRH8CUY@IUC\J9CUN TJ D e£^ NPT+C2I o¥ m q Ê © J9TRH Ê ó @>J9BY D @^ D @>Ih@TC0JB2G Ih@>HD M/NQC D IhC\JXCUN TRJ D e^ NQT+C2[ACUY@T¶CZY+@]IhC\JXM/GQ@W JXT+N v GZH¯ ë fpÊ © m Ê © YRJ/IÔC D JXTIUt@ D Ih@NQTCU@ D Ih@BCUN T a NQCUY¯CUY@§KTRIhC\JXM/GQ@ W JXT+N p GH¡ fpÊ ó m Ê ó où Ï &3»;þj« D IU@> ú W J9GQ@t@BC D=E @GZH&IJ D @IhC D KBCUK D J9GQGQexIUC\JXM/GQ@ o

ù Ï &3»;þ q T H;N W @TRIhN TRI2-l;R;3 å IhC D KB;CUK D J9GQGQe=IhC\JXM/GQ@¤t@BC DE @GHLNIR« D IU@> ú W JXGQ@ oq C a0 KGZHM/@)B Tt@TNQ@TC=N CUYNZI a @ D @bJ9GZI CUY@)B;J/Ih@)NQTÔYN | Y@ D H;N W @TRIhN TRI\[SM/KCJ9GJ/I[CUYNZI¤NZI¤T CCUY@xB;J/Ih@ o lY+@ D @x@"NZIUCnIUC D K+BCZK D J9GQGPedIhC\JXM/GQ@8t@BC D0E @GZH&IFNQTH;N W @TRIhN TI ≥ ¥a Y IU@ÆT T a J9TRH;@ D NQT | IU@CbNZIbCUY@Æ@TCUN D @H W JXNQT f CZY+@nI ·B;J9GPGQ@>H¤4c a I mpo

7 ¨±F+ ºð O¶43»&° ' 4 R 7 #93;ly º# Ï 4u&q C a¤ KGZHzM/@ D J9CZY+@ D B W ^&GQNQB;J9CZ@>HzC H;@>IUB D NQM4@@uJ9BCUGQeY a J9GQGCZY+@IUC\J9CZN TRJ D e^ NQTC\InJ9TRHBG Ih@>H D M/NQC2I J0« D Ih@> ú W J9GQ@Lt"@B2C DE @GZHNQTbT¾H;N W @TRIhN TRI f CUYNQTr T = D ¥ m E CC | @CUY@ D o çyKCNQCNZInJ D @ W J D rjJXM/GQ@ JXB2CCZYJXC« D IU@> ú W J9GQ@t"@B2C DE @GZH&InB5JXTÝM4@¿H;@B W ^ IU@>HbNQTC IhN W ^&GQ@¶^&NQ@B@>I[@>J9BY =a YNQBYB D2D @>IU^ TH>IRC J¤B D NQCUNPB5JXGu@GP@ W @TC oãl@C k 5 H;@T CZ@LCZY+@0KTNQCRMJ9GPGuNQT 5 J9GQGu^ NQTC\IJ9CFJnH;NIhC\JXT+B@ ≤ ¤pD W CZY+@ D N | NQT o ãl@C ú ©H;@T CU@LCUY@LKTNQCBN D B2GP@LNQT ó J9GQGu^ NQTC\IJ9CJH;NZIUC\J9TB@ @uJ9BCUGQe pD W CUY@ D N | NQT oi D @>J9BY¯IUC\J9CZN TJ D e¶^ NQTC a NQCUY¾KTIUC\J9M4GQ@W JXT+N v GZH H;N W @TRIhN Trj[ a @ a NPGQG*KRIh@ T@M/KNQGZH;NPT | M/G Br CZY+@ pD W k × k ¡ −

f J YRJ9TRH;GQ@ 2mpo¶i D @>JXB2Y B2G IU@>H D M4NQC a NPCUYKTIUC\J9M4GQ@ W J9TN p GZH H;N W @TRIUN Trj[ a @ a NQGPGKRIh@ T+@¤M/KNQGZHNQT | M/G Br CUY@ pD Wú © × k − © × k ¡ −

f J D KTHVYRJ9TRH;GQ@ 2mpo çeC\JXruNPT | CZY+@nK+TN T CUY@>Ih@M4K+NQGH;NQT | M/G BrjI[a Y+NPB2Y®J D @JXGQG a @>HC NQTCU@ D Ih@BC TGQe]J9G T |Ih^>@B2N E @>HL^J D C\I CZY+@N D M KTRH&J D NQ@>I[ a @LB;J9TD @B TRIUC D K+BC NQTÐJ]C ^ G | NQB;J9G³Ih@TRIh@ CUY@D N | NPTJXGu« D Ih@> ú W J9GP@0t"@BC DyE @GZH o

Page 20: Notes on the Topology of Vector Fields and FLows

Á ¢£ CU@>I TCUY@0 ^ G | e ?A@BC D i NQ@GZH&IJXTH i G a I

ù Ï L±F435#ª 443»l;35 ðg TRIhNH;@ D J« D Ih@> ú W J9GQ@¤t@BC DE @GHL? o6 :;35R4#ª ¬<&þdãl@C Ê © [ Ê ó [FJ9TRH Ê õ M/@B D NPCUNQB;J9GÑ@GQ@ W @TC\I ? o ú K^&^ IU@ CUYRJ9C¡ fpÊ © m ∩ ë fpÊ ó m ≠ ∅ [4J9TRHVJXGZI ¡ fpÊ ó m ∩ ë fpÊ õ m ≠ ∅ o lY+@TNPC W KIUCLJ9GZI M/@¤C D K@0CZYJXC¡ fpÊ © m ∩ ë fpÊ õ m ≠ ∅ o ú CZY+@ D @8NZILJ£rsNQTH C D J9TRIhNQCZNQtNPCUe ^&@ D J9CZNQT | Y+@ D @ o6 :;35R4#ª ¹ þ ú K^&^ IU@VNQTRIhCZ@>J/HVCUYRJ9C a @YRJ9t"@ÔB D NQCUNPB5JXG@GQ@ W @TC\I Ê © J9TRH Ê ó ?a NQCUY¡ fpÊ © m ∩ ë fpÊ ó m ≠ ∅ [/JXTHJ9GZI ¡ fpÊ ó m ∩ ë fpÊ © m ≠ ∅ o lY@TwNPC W KRIUC p GZG a CZYJXC Ê © = Ê ó o¢£a GP@C Ê © J9TRH Ê ó M/@VJXT+e£C a0 B D NPCUNQB;J9Gu@GQ@>W @TC\I JÝ« D Ih@> ú W JXGQ@Ôt@BC DE @GH§? olY@T a @IUYJXGQGsKIU@0CZY+@¤T C\J9CZN T Ê © ≤ Ê ó C W @>JXTCUYRJ9Cl¡ fpÊ © m ∩ ë fpÊ ó m ≠ ∅ oi D W CUY@C a0 M+Ih@ D tJXCUN TRIVJXM t"@>[ a @¨IU@@CUYRJ9CxCUY@wB TRH;NQCUN T­CUYRJ9C ≤ NZI¨JM TJ E H;@^J D CUNJ9G D H@ D NQT | TCZY+@¨Ih@C B D NQCZNQB;J9G*@GQ@>W @TC\I ? ok @>IhB D NQM/NQT | J« D IU@> ú W J9GQ@¤t@BC DE @GHLM4e Ú :; ºSð # Ï 7 35 #ª 7 ;;;#9 7/7 3»u ð#9

<3¨#9# 43 å ±F #¤43 7 +&3¸: #¹ ¨u º; 441R# Ï ³#9:²

4 º1\ª% ¨ º1 7 &ê435:² º#9-à Ï # Ï ;3~3#

#9:²zS º1\ y#ªàx #9&l->© Ú ±F 7 º å ºð# Ï À±F º3sª:d<«: ¹1\3à Ï 7 Ï :d< ≤ : ¹|" @>ILJG T |Va J9eVC a J D H&IB T+t"@eNPT | Jt"@ D e|" H)H;@>IhB D NQ^&CUN T a YRJ9CLCZY+@t"@B2C DE @GZH?wNZIH NPT | C ^ G | NQB;J9GQGQe o

f ¢£ CZ@>[Y a @t"@ D [CUYRJ9CdCUY@ D @bNZI¿IUCUNQGPGJ/H&H;NZCUN TJ9G8C ^ G | NPB5JXGnNQT pD W J9CZN T Ï à CUY@IhC2J9M/GP@ÐJ9TRH`KTIUC\J9M4GQ@ W J9TN p GZH&INPT+CZ@ D IU@B2C@>J9BY CUY@ D CUYRJ9CNZIwT CB t@ D @>H¾NPT¬CZY+@J9M t@nH;@>IhB D NQ^&CUN T oËm¹ ©n å O¶43»&° ' 4Lyਫ D IU@> ú W J9GQ@ c a I J D @ N W ^ D C\JXT+C C KTH;@ D IUC\J9TRH&[ M/KC CUY@e D @^ D @>Ih@TC T@@"C D @ W @ J]IU^&@B2C D K W o lY+@T T a J9TRH;@ D NQT | IU@C J« D Ih@> ú W J9GQ@¿t@BC D¨E @GHNIB T+B@TC D J9CU@>H³NQT¶J E T+NQCZ@³T+K W M4@ D£Á J9TRH pH;N W @TRIhN TRJ9GIU@C\I CUY@IUC\J9CUN TJ D e)^ NQTC\IJ9TRH0B2G Ih@>H D M/NQC\I o CCUY@ ^&^ IhNPCU@@"C D @ W @J D @CUY@À+â4à W @TCUN T+@>HÀNPT ú @B2CZN T 6 o lY@T TRa J9TRH;@ D NPT | Ih@C J9T T I tÝc a NZICUY@@TCUN D @H W J9NPT CUY@c a o THÀCZY+@ D @NZI³JrsNQTRH Ye^&@ D M GPNQB2NPCUe a Y+NPB2Y)J9^&^&GQNQ@>IC CZY+NZI@TCUN D @T TR a J9TRH;@ D NQT | Ih@C @>J9BY¿^ NPT+CLYRJ/IJdIU@C IhC2J9M/GQ@H;N D @BCUN TI¤@ W J9TRJ9CZNQT |pD WNQC2[ T a YNQBY¨CUY@c a NZI B TC D J9BCUNPT | [ J9TRHJ¨Ih@C K+TRIUC\J9M/GP@)H;N D @BCUN TRI T a YNQBY¿CUY@c a NZI @^JXTH;NPT | oÄ TRHCUY@¿B T+B@^&C Y+e"^&@ D M GQNQBNQCZe®B;J9TM/@@"CU@TRH;@>HVC NPT+BGQKRH;@ÀJ W KB2Y a NZH@ D tJ D NP@CUe Ih@C\ICZYJXT W J9TN p GH&I o )Y+@T¨CZY+NINZIH T@^ D ^&@ D GQe9[CUY@ D @>IUKGQCUNQT | c a IJ D @>[GQNQrs@« D IU@> ú W J9GQ@Õc a I\[IhC D KBCUK D J9GQGQe IhC\JXM/GQ@ o«dK+BY^ D|D @>II£YRJ/IM4@@T W J/H;@>[AM/KCxJ/I GZJ9CZ@ 66 IhKBYI ·B5JXGQGQ@>H: 7 ;#9¤J D @ J DpD W M/@NQT | B W ^&GQ@CZ@GQe£BGZJ/I\IhN E @>H o¹ < y35# Ï ;33»&+01 ' #ª åÃ*T+@ E BCUN T a @áYRJ9t"@_J/IIUK W @>H´C J9t NHB W ^&GQNPB5JXCUN TRI=NPT§CZY+@>IU@)T CU@>I[NZI³CUYRJ9CVCUY@H W JXNQT Jxt"@BC D8E @GZH W KIUC¤M/@¨JXT ^&@TIh@CNQT KB2GQNH;@>J9T¯Ih^JXB2@ o çyKCÀNQT J9BC\[yCUY@

Page 21: Notes on the Topology of Vector Fields and FLows

¢£ CZ@>I TCUY@¤ ^ G | e ?@B2C D i NQ@GZH&IJXTH i G a I ++

TRJ9CUK D J9GH W J9NPT pD J®t"@B2C D¿E @GZHÔNIJ9TJ D M/NQC D J D e£TpHN W @TRIhN TRJ9G W J9T+N p GZH oÃ*TÀCUY@ T+@LYJXTH&[;CZY+@ W J9CZY+@ W J9CUNQB;ISNZISKIUKJ9GQGPe W IUC@GQ@ | J9TCN CUY@VH W JXNQT J0t"@BC DE @GZHNZIJB W ^AJ9BC W J9TN p GZH a NQCZY KCM KTRH&J D e9[4JXTH¤N CZY+@t@BC DE @GZH¤NZIlCUN W @>·NQTRH;@^&@TRH;@TC f GQNPru@ CZY+@ T@>I a @ YRJ9t@ M4@@TB TIUNZH;@ D NQT |£pD W IhC CUY@>Ih@¤T CU@>I mpoçyKCNQT D @>J9GQNQCZe9[sH W JXNQTRI pDD @>J9G a0D GZH£t@B;C DE @GZH&IJ D @ W IUCdB WW T+GPe W J9TN p GZH&Ia NQCUYM KTRH&J D e9[jJ9TRHt"@BC DE @GZH&I p K+TRHNPTCUY@ D @>JXG a¤D GZHJ D @ pD @O/K@T+CZGQeCUN W @>pH;@^&@TRH;@TC o«dK+BYwNQTCUY@¨IJ W @ a J9eCZYJXC0CZY+@ Ò NQTB5J DK#W JX^B5JXTM/@KRIh@>HC KTRH;@ D IhC\JXTHCZY+@ D M/NQCIhC D KBCUK D @ J D K+TRH J BG IU@>H D M/NQC2[~CZY+@H;e"TJ W NQB;I W J9^>^&NQT | INPT | @T@ D J9GIUY+@>H&IJ|"D @>JXCH;@>J9G GQN | YC T¬CUY@H;e"TJ W NQB;I c a I\[/J9TRH0NZI a @GQG a0D CUYe K D CZY+@ D IhCZKH;e o?A@ D eGQNQCZCUGQ@NZIxrsT a TÐJ9M K+C a YRJ9C=rsNQTH H;e"TJ W NQB;I D @>J9G a0D GZHt"@BC D³E @GH&ICU@TRHC J9BCUKRJ9GQGPexYJXt@>[ pD @uJ W ^&GQ@NPTJ9@ D H;eTRJ W NQB;I o ?SJ9GQKRJ9M4GQ@^ D|"D @>I\IxB KGZHM/@ W J/H;@M4eB D @>JXCUNQT | I C a J D @¤C H;@CU@BCRC ^ G | NQB;J9G @>J/CUK D @>I ØD @>J9GZ a¤D GH t@BC D E @GH&I[¾J9TRHD @^ D CUNQT |® T~CUY@¿ruNPTH&I E @GZH&I@TB KTRCU@ D @>H o«dK+BY ^ D|"D @>I\IÝB KGZHÕJ9GZI M/@ W J4H;@ØM/eH;@t"NZIhNPT | T+@ a [ D2 K | Y¿H;@>IUB D NQ^&CZN TRI Y a Jt"@B2C DE @GZH¤c a IFJ D2 KTRH&[XB W ^&KC\JXM/GQ@ a NPCUYJ W H;@ D TB W ^>K+CZ@ D [uJ9TRH a YNQBYwJ D @ D M/KRIhC@T K | Y®C M/@¿J9BBK D J9CZ@¿H;@>Ih^&NPCU@TK W @ D NQB;J9GN W ^ D @BNZIUN T o@nIhYRJ9GQGjIh@@ o