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M-Files and Control Statements

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Prof. Dr. İrfan KAYMAZ

Computer Programming in

MATLAB

Atatürk University Engineering Faculty

Department of Mechanical Engineering

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M-File (script file) file is a text file containing Matlab commands, one per line (or separated by a comma or semicolon).

In order for Matlab to recognize your script file, it must be saved with .m

extension and it must be saved in a location within the Matlab search path.

Script files consist of a collection of Matlab commands.

From now on, write a script for every exercise!

Opening M-files

M-Files

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Necessity for M-Files If there are a lot of variables, it will be very complicated to assign all the

variables in the command window. it will be easy to change the program in m-file. M-files can be easily reopened and edited.

M-Files

Name of M-Files The rules for script file names are the same as those for MATLAB variable

names. M-file must be in the current folder. Name of the M-file does not contain any Turkish letter. Name of the M-file can not be the Matlab functions like (pi, exp, sin…). Any variable name which was used in m-file must not be given for a file

name.

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M-Files and Control Statements Current Directory

To run a script file, it is necessary that

current directory is set to the directory

in which the script is saved.

To change the current directory, click

on the browse button (…)

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M-Files and Control Statements First M-file

To run a script file, make sure

that the file is saved into the

current directory and then click

on the run icon.

(Please note that the file name

is first.m)

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M-Files and Control Statements input(‘’)

Input command enables us to assign a value to a varaible.

Whatever comment is writen between the quotation marks is displayed to the screen, and the user must enter an appropriate value.

X=input(' Comment ');

x= input('Input the value of x: ')

Input the value of x :

x =

10

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M-Files and Control Statements input(‘’)

After running the input(‘’) function, you must input a value from the command line.

By using input(‘’) function, you can make your program interactive by asking the user to enter a value which is used in your program.

Example: R = input(‘Please enter the radius of circle: ‘) After the user enters the value from the keyboard, the software assign that value to the variable called R. Note: MATLAB program is case-sensitive.

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M-Files and Control Statements Example 1

Write a Matlab program to calculate the area and perimeter of a circle by entering the radius of circle from the keyboard.

R = input(' Enter the radius of circle ');

area=pi*R^2;

perimeter=2*pi*R;

area

perimeter

Solution:

Note that the area and perimeter variables are at the end of program and there is no semicolon after them to print the results.

If you put the % sign in front of any line in your program, that line will not be executed. This text is normally used to include comments in your code such as:

% The purpose of this routine is to compute

% the value of ...

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Write a Matlab program to calculate the value of the following equation by entering x and y from the keyboard.

4

10

32 3yx

)(log

1)ln(yxyxyxy)F(x,

y

yx

y

x

Note: Variable names do not contain punctuations except underscore.

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M-Files and Control Statements Matlab Operators

There are two main operators in Matlab; Relational and Logical operators

Relational operators are used to compare variables.

Relational operators perform comparisons between two elements or element-by-element comparisons between two arrays.

The result of a comparison is either TRUE (1) or FALSE (0)

If the relation is true, then elements set to logical 1 (true), and If the relation is not true, then elements set to logical 0 (false).

1- Relational Operators

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M-Files and Control Statements Relational Operators

== Equal to

~=

Not equal to

>

Greater than

>=

Greater than or equal to

<

Less than

<=

Less than or equal to

a==b → 0

a==c → 1

a~=b → 1

a~=c → 0

b>a → 1

a>c → 0

b>=a → 1

c>=b → 0

a<b → 1

a<c → 0

a<=b → 1

b<=c → 0

a=5, b=6, c=5

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M-Files and Control Statements Relational Operators

When we control the equality, we use double == symbols.

When we assign a value to any variable, we use single = symbol.

For example, if you write 3=5 into the command line, MATLAB gives an error. But if we write 3==5 to the command line, it means a question: is 3 equals to 5 ? The result is false, it produces “0” as an answer.

>> 3==5

ans =

0

>> >> 3=5

??? 3=5

|

Error: The expression to the left of the

equals sign is not a valid target for an

assignment.

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M-Files and Control Statements Logical Operators

Logical operators are used to combine variables.

There are four logical operators;

► "AND"

► "OR"

► "XOR"

These operators are ralated with two relational operators,

binary

► "NOT" This operator is related with one relational operator,

unary

2- Logical operators

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Name Symbol Example with

symbol Text description

NOT ~ ~A True if A is false

AND & A & B True if both A and B are true

OR | A | B True if either A or B (or both!) are true

XOR True if either A or B (but NOT both!) are

true

The following table shows the results of four different pairs of input values to the logical operators above:

A B ~A ~B A & B A | B xor(A, B)

0 0 1 1 0 0 0

0 1 1 0 0 1 1

1 0 0 1 0 1 1

1 1 0 0 1 1 0

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Example:

>> k=4; m=5;

>> (k>6) & (m<8)

ans = 0

>> (k>6) and (m<8) |

Error: Unexpected MATLAB expression.

If you want to write

0<=x<9 in Matlab, type

(0<=x) & (x<9)

or

x>=0 & x<9

but not,

x=>0 & x<9

Operator Name

& AND

| OR

xor XOR

~ NOT

A = [0 0 pi eps] and B = [0 -2.4 0 1],

C = xor(A,B)

C =

0 1 1 0

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if conditional statement can be used to control conditionally the execution of statements.

As a result of a comparison, selected blocks of program are executed or skipped.

Control Statements

Conditional statements: if-end, switch-end

if expression 1. statement; 2. statement; end

1 2 3 if expression 1. statement; else 2. statement; end

if expression 1. statement; elseif expression 2. statement; else 3. statement; end

There are three different usage:

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Write a Matlab program that asks the user for an x and y value and then computes

the following functions according to the following scheme:

2

23/1

lnlog)(0

2)(0

x

xxxfx

yxe

yxxfx

x

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Write a Matlab program that asks the user for an x value and then computes the

following functions according to the following scheme:

2xF(x)

xF(x)

1 < = x < 10

x > =10

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x>y, A1= (x-y)

x=y, A2= (x+y)7

else, A3= x+y

Write a Matlab program that asks

the user for an x and y value and

then computes the following

functions according to the

following scheme:

x=input('x value=');

y=input('y value=');

if x>y

A1=sqrt(x-y)

elseif x==y

A2=(x+y)^7

else

A3=x+y

end

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M-Files and Control Statements Homework 1

In a cargo company, a pricing policy according to the package weight is as follows;

Base price is 5 TL for packages up to 2 kg. For packages heavier than 2 kg, 0.5 TL should be added to the base price for every 1 kg. If the packages are heavier than 35 kg, 10 TL should be added to the total price. The packages heavier than 50 kg are not accepted because of worker’s health.

Write a Matlab program that asks the user for package weight and then computes the price according to the above-mentioned scheme.

(Assume that the scale readings are only integer values)

Weight (kg) Price (TL)

1 5

2 5

3 5.5

4 6

… …

50 39

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M-Files and Control Statements Next Lecture

Control statements - Conditional statements: if, else, elseif, switch - Repetition statements: while, for

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