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Introduction to Programming in

MATLAB

Intro. MATLAB Peer Instruction Lecture Slides by Dr. Cynthia Lee, UCSD is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License.

Based on a work at www.peerinstruction4cs.org.

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SCRIPTSAre your fingers tired of typing things again and again? Trying writing…

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Using Scripts

• I entered some important data about my dog Diablo into MATLAB, including: – Her name (‘Diablo’) – Her weight (22 kg) – The radius of her torso (15 cm)

• I now want to calculate the circumference of her circular-shaped torso, using a script.

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Variable Scope in Scripts

Circumference.m (script)d = 2 * r;circumf = pi * d;

Command Window» d = ‘Diablo’; » w = 22;» r = 15; » Circumference» circumfcircumf =

94.2478» d

I entered some data about my dog Diablo into MATLAB, including her name (Diablo), weight (22kg) and the radius of her torso (15cm). I now want to calculate the circumference of her

circular-shaped torso, using a script.

What is printed here?

a) 30b) Diabloc) Other/None/Error

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FUNCTIONSAnother way to save yourself some typing:

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What is the role of the pink part of the function definition line?

Circumference.m (function)function [ circumf ] = Circumference( r )d = 2 * r;circumf = pi * d;end

a) It tells you that you need to assign the input value to a variable named r before you call the function Circumference.

b) It tells you that Circumference takes one input, called r.c) It tells you that Circumference will output a value in a variable

named r.d) It tells you that Circumference returns the value of r.e) None/more than one/other

Which is NOT a valid way to call the Circumference function from the

Command Window?Circumference.m (function)function [ circumf ] = Circumference( r )d = 2 * r;circumf = pi * d;end

» circumf = Circumference(10);» Circumference(10);» c = Circumference(10);» x = 10; » c = Circumference(x);None/More than one/Other

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a) b) c) d)

e)

Comm

and Window

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Variable Scope in Functions

Circumference.m (function)function [ circumf ] = Circumference( r )d = 2 * r;circumf = pi * d;end

Command Window» d = ‘Diablo’; » w = 22;» r = 15; » circumf = Circumference(r)circumf =

94.2478» d

I entered some data about my dog Diablo into MATLAB, including his name (Diablo), weight (22kg) and the radius of his torso (15cm). I now want to calculate the circumference of his

circular-shaped torso, using a function.

What is printed here?

a) 30b) Diablo

c) Other/None/Error

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(a) Functions work this way, OR (b) Scripts work this way

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(a) Functions work this way, OR (b) Scripts work this way

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Variable Scope in Functions

Circumference.m (function)function [ circumf ] = Circumference( r )d = 2 * r;r = ‘messing with r’;circumf = pi * d;end

Command Window» d = ‘Diablo’; » w = 22;» r = 15; » circumf = Circumference(r)circumf =

94.2478» r

I entered some data about my dog Diablo into MATLAB, including his name (Diablo), weight (22kg) and the radius of his torso (15cm). I now want to calculate the circumference of his

circular-shaped torso, using a function.

What is printed here?

a) 15b) messing with rc) messing with r 30

d) Other/None/Error

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Scripts vs. FunctionsScripts• Location: in a file (file’s name will

be how you call the script)• Use: type script name in the

Command Window• Input/Output: must be careful to

have variable(s) with certain names set to input values before calling, then look at variable(s) with certain names to see what happened/output

• Variable scope: script has full access to all variables as if its code had been just typed in the Command Window

Functions• Location: in a file with same name as

the function• Use: type function name in Command

Window, include assignment of output and/or include input arguments

• Input/Output: input(s) are provided as specified arguments, output(s) are provided as specified return values

• Variable scope: function has no access to read any variables from the Command Window, except as they are explicitly provided in the input arguments. Function has no access to change/write to any variables to the Command Window, except as explicitly given in the outputs