ME 102 Mechanical Engineering Orientation

Class Notes

by

Prof.Dr.Nevzat Onur

Introduction to MATLAB

for Mechanical Engineers

Cankaya University

Faculty of Engineering

Mechanical Engineering Department

1-2

Entering Commands and Expressions

• MATLAB retains your previous keystrokes.

• Use the up-arrow key to scroll back through the

commands.

• Press the key once to see the previous entry, and

so on.

• Use the down-arrow key to scroll forward.

• Edit a line using the left- and right-arrow keys

the Backspace key, and the Delete key.

• Use the down-arrow key to scroll forward

• Press the Enter key to execute the command.

Scalar arithmetic operations

1-6

1-7

Order of precedence

1-9

% designates comment .Matlab does not execute it

keskin

Keskin

KESKIN

Keskin_1

Keskin_2

>> r=8;

>> h=15;

>> V=(pi*r^2*h)/3

V =

1.0053e+03

Numeric

display

formats.

Some commonly used mathematical functions

1-20

21

exa

abs(z) The absolute value of z=x+iy angle(z) the angle of z. This is calculated by atan2(y,x)

Example

Given z=3-5*i

>> real(z)

ans =

3

>> imag(z)

ans =

-5

>> abs(z)

ans =

5.8310

>> angle(z)

ans =

-1.0304

25

>> a=30;

>> b=20;

>> A=sqrt(b^2+16*a^2)/2;

>> B=(b^2/( 8*a ))*log((4*a+sqrt(b^2+16*a^2))/b);

>> s=A+B

>>s =

64.9806

COMMENTS

% -the comment symbol

The comment symbol may be put anywhere in the

line. MATLAB ignores everything to the right of the

% symbol. For example,

>>% This is a comment.

>>x = 2+3 % So is this.

x =

5

Note that the portion of the line before the % sign is

executed to compute x.

Some Input/output commands

disp can be used to display the value of a variable.

>> x=3.0;

>> y=3^x;

>> disp(y)

27

Example

>> disp(' And now for something completely different' )

And now for something completely different

Example

>> disp('----------------------------------')

----------------------------------

29

You can perform operations in MATLAB in two ways:

1. In the interactive mode: all commands are entered

directly in the Command window,

2. In the script file mode: By running a MATLAB program

stored in script file. This type of file contains MATLAB

commands, so running it is equivalent to typing all the

commands—one at a time—at the Command window

prompt. You can run the file by typing its name at the

Command window prompt.

30

Example:

Write a script file for the following

problem and save it as T5

>> T5

Part a

Lp =

92.0412

Part b

m =

7.9057

>> sphere

Enter radius=5

Surface area of sphere

314.1593

Keep in mind when using script files:

1. The name of a script file must begin with a letter,

and may include digits and the underscore

character, up to 63 characters.

2. Do not give a script file the same name as a

variable.

3. Do not give a script file the same name as a

MATLAB command or function. You can check to

see if a command, function or file name already exists by using the exist command.

39

40

diary

Diary command saves your input to MATLAB and most

of the output to disk. This command toggles diary on and

off. (If no file is given, it is saved to the file diary in the

current directory.)

diary on turns the diary on.

diary off turns the diary off.

41

1)

Write script file.

2)

Write a script file for this problem

Write a script file