the berge mystery story presented by supriya janjanam
TRANSCRIPT
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The Berge Mystery Story
Presented bySupriya Janjanam
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Outline
• A Mystery in the Library & Facts
• Interval Graph
• Properties
• Solving the Mystery
• References
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A Mystery in the Library
Six professors has been to the library on the day that the rare tractate was stolen.
Each has entered once, stayed for sometime, and then left.
If two were in the library in the same time , then at least one of them saw the other.
Detectives questioned the professors and gathered the following testimony :
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The Facts: Abe said that he saw Burt and Eddie
Burt said that he saw Abe and Ida
Charlotte claimed to see Desmond and Ida
Desmond said that he saw Abe and Ida
Eddie testified to seeing Burt and Charlotte
Ida said that she saw Charlotte and Eddie.
ONE OF THE PROFESSOR LIED!! WHO WAS IT?
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Interval Graph
A graph is an interval graph if we can find intervals on the line so that two vertices are joined by an edge if and only if their corresponding intervals overlap.
Phase 1
Phase 2
Phase 3Task 4
Task 5
1 2 3
4 5
The interval graph G
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Interval Graph
v1 v2
v3v4
v1 v2
v3
v1v2
v3v1
v2v4
V3??
An interval graph NOT an interval graph
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Applications of Interval Graphs
• Genetics
• Scheduling
• Artificial intelligence
• VLSI design
• Computer storage
• Frequency assignment
• More …
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Properties of Interval Graph
• Two properties characterize interval graphs:
- The Chordal Graph Property
- The co-TRO Property
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The Chordal Graph Property
Every cycle of length > 4 has a chord
i.e., they may not contain chordless cycles!
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Interval Graphs are Chordal
Interval graphs may not contain chordless cycles!
- i.e., they are chordal. Why?
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Interval Graphs are Chordal
Interval graphs may not contain chordless cycles!
- i.e., they are chordal. Why?
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The co-TRO PropertyThe transitive orientation (TRO) of the
complement
i.e., the complement must have a TRO
Not transitive ! Transitive !
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Solving the Mystery
Abe said that he saw Burt and EddieBurt said that he saw Abe and IdaCharlotte claimed to see Desmond and IdaDesmond said that he saw Abe and IdaEddie testified to seeing Burt and CharlotteIda said that she saw Charlotte and Eddie.
The Testimony Graph
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Solving the Mystery
Clue 1:
Double arrows imply TRUTH
The Testimony Graph
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Solving the MysteryUndirected Testimony Graph
cycle
We know there is a lie, since {A, B, I, D} is a chordless 4-cycle.
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Intersecting Intervals cannot form Chordless Cycles
Burt Desmond
Abe
Here No place for Ida’s interval:It must hit both B and D but cannot hit A.
which is Impossible!
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Solving the Mystery
There are three chordless 4-cycles:{A, B, I, D}{A, E, I, D}
{A, E, C, D}
One professor from the chordless 4-cycle must be a liar.
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Solving the Mystery
There are three chordless 4-cycles:{A, B, I, D}{A, E, I, D}
{A, E, C, D}
Burt is NOT a liar: He is missing from the second cycle.
One professor from the chordless 4-cycle must be a liar.
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Solving the Mystery
There are three chordless 4-cycles:{A, B, I, D}{A, E, I, D}
{A, E, C, D}
Ida is NOT a liar: She is missing from the third cycle.
One professor from the chordless 4-cycle must be a liar.
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Solving the Mystery
There are three chordless 4-cycles:{A, B, I, D}{A, E, I, D}
{A, E, C, D}
Charlotte is NOT a liar: She is missing from the second.
One professor from the chordless 4-cycle must be a liar.
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Solving the Mystery
There are three chordless 4-cycles:{A, B, I, D}{A, E, I, D}
{A, E, C, D}
Eddie is NOT a liar: He is missing from the first cycle.
One professor from the chordless 4-cycle must be a liar.
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Solving the Mystery
Burt is NOT a liar: He is missing from the second cycle. Ida is NOT a liar: She is missing from the third cycle. Charlotte is NOT a liar: She is missing from the second. Eddie is NOT a liar: He is missing from the first cycle.
WHO IS THE LIAR? Abe or Desmond ?
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Solving the Mystery
WHO IS THE LIAR? Abe or Desmond ?
If Abe were the liar and Desmond truthful, then {A, B, I, D} would remain a chordless 4-cycle, since B and I are truthful.
Therefore:
Desmond is the liar.
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References
[1] http://www.cs.haifa.ac.il/~golumbic/courses/algorithmic-graph-theory/slides_and_notes_of_lectures/Lecture%201%20-%20Introduction/intro-agt-v1b-part1.pdf
[2] https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CB4QFjAA&url=http%3A%2F%2Fliawww.epfl.ch%2FTeaching%2FCourses%2FAlgorithmicGraphTheory%2Fdoc%2FRAT-thailand.ppt&ei=RGNFVOzKNdSwyATMs4K4BQ&usg=AFQjCNFtXDmvuMXAftqXMkqltQ8AGkLqpA&sig2=muUpMdF2FPCr9pKAxgKrQQ&bvm=bv.77880786,d.aWw&cad=rja
[3] https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=4&ved=0CDcQFjAD&url=http%3A%2F%2Fwww.dis.uniroma1.it%2F~seminf%2Fseminars%2Fgolumbic.ppt&ei=RGNFVOzKNdSwyATMs4K4BQ&usg=AFQjCNGS79daY-KflIW7ErRF1jaM_vIR-w&sig2=oPFk-4Si8FwLYESjmtQaYQ&bvm=bv.77880786,d.aWw&cad=rja
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ANY
QUERIES….???
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Thank you…