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College of EngineeringEngineering Education Innovation Center

Introduction to MATLAB

Alternative MATLAB Introduction Lecture authored by Annie Abell

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MATLAB is a powerful program for numerical computations, plotting and programming.

• Use it as a calculator.• Define variables and use them in calculations.• Use built-in functions.• Plot graphs.• Write and run computer programs.• Perform symbolic mathematics.

Introduction to MATLAB

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Click on the shortcut icon or select: start / All programs / MATLAB

There will be a fairly long initialization process, then following prompt should appear in the command window:

>>

Open MATLAB now:

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Command Window (where commands are entered)

Command History (what has been typed)

Workspace (variable values)

Command prompt

Current Directory (lists file, etc.)

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MATLAB’s Working DirectoryWhen you first start MATLAB it is a good practice to change the working directory to your Z: drive or USB device.

Keep all of your files in the same folder so you do not have to constantly change your directory

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Order of PrecedenceHigher-precedence operations are executed before lower-precedence operations (like Excel or graphing calculators).

If two operations have the same precedence, then the expression is executed from left to right.

PRECEDENCE OPERATION

First Parentheses (innermost pair first)

Second Exponentiation.

Third Multiplication and division

Fourth Addition and subtraction

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Precedence of Operations

>> 7 + 8 / 2 ans =

11

…not what we wanted

>> (7+8)/2 ans =

7.500

… correct!

Task : Find the average of 7 and 8

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Task: Add the cube root of 27 to the 5th root of 32

>> 27 ^ 1/3 + 32 ^ 0.2 ans =

11 … not what we wanted

>> 27 ^ (1/3) + 32 ^ 0.2 ans =

5

Precedence of Operations

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>> x = 5x =

5

>> x = x + 5 x =

10

This statement does not make any mathematical sense but in programming language it changes the value of ‘x’ to a new value.

Variable Definition

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We can use the variables defined previously to do calculations.Define the following: a=8, my_var =12

>> a + my_varans =

20

>> a * my_var^2ans =

1152

Calculations with Variables

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• Can be up to 63 characters long.

• Must begin with a letter.

• Can contain letters, digits, and the underscore character (no spaces).

• MATLAB is case sensitive; it distinguishes between uppercase and lowercase letters.

• Avoid naming variables with names that are used by MATLAB: exp, sin, cos, sqrt, length, mean, max, min…

Rules About Variable Names

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Acceptable:My_nameMyNamemyname1

Unacceptable:1Name starts with numeralMy Name spaces not allowedMy-Name special characters not allowed

Examples of Variable Names

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exp(x) exponential (ex)

log(x) natural logarithm (log base 'e')

log10(x) base 10 logarithm (log)

sqrt(x) square root

abs(x) absolute value

Built-In Math Functions: Examples

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In MATLAB, trigonometric functions use radians. So for these examples, x is in radians:• sin(x), cos(x), asin(x), acos(x), tan(x),

cot(x)

MATLAB also has equivalent functions where x is in degrees:• sind(x), cosd(x), tand(x), etc

Built-In Math Functions

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Task: calculate sin(∏ / 2). Note: ∏ is defined by MATLAB as pi.

>> sin(pi/2)

ans =1

Built-In Math Functions: Examples

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Task: calculate e2

>> e ^ 2??? Undefined function or variable 'e'

How do we fix this?

>> exp(2)ans =

7.3891

Built-In Math Functions: Examples

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Built-In Math Functions: Examples

Task: calculate sin2x, where x = ∏ /4

>> x = pi/4 x =

0.7854

>>sin(2*x) ans =

1

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Task: Using (cos2xsin2x + tan(x/2)) / e3x , find the value for x = 30 degrees.

>> x = 30 x =

30

>> x = x * pi / 180 x =

0.5236

Built-In Math Functions: Examples

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Task: Using (cos2x sin2x + tan(x/2)) / e3x , find the value for x = 30 degrees.

>> (cos(2*x)* sin(x)^2 + tan(x/2)) / exp(3*x) ans =

0.0817

Built-In Math Functions: Examples

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• Once the script file is completed, it must be saved. In our class use Save As to your Z:\ or your own USB drive.

• This should be the same as the working directory you specified when you started MATLAB.

• ALWAYS SAVE YOUR WORK. Back it up in multiple places for safety! To the cloud!!

Saving a Script File

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Valid File Names• Prob1a.m• Prob1a.m• problemone.m

Invalid File Names Prob-1a.m Special Characters not

allowedProb 1a.m Spaces not allowed1aProb.m Cannot start with number

Saving a Script File

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To clear the command window: clc>> clc

To clear all variables previously defined: clear>> x = 5 x =

5>> clear>> x ??? Undefined function or variable 'x'

Useful Programming Commands

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This function displays a message to the command window. It can be a string of text or variable contents.

To display your message as text, use single quotes around your message:

>> disp(‘Brutus Buckeye’) Brutus Buckeye

The Display Function: disp()

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To display any variable contents, do not use quotes:

>> x = 5 x =

5>> disp(x) x =

5

The Display Function: disp()

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Suppressing Output

This is good practice! You don't need all of your program displayed in the command window, just the relevant info.

>> x = 6 x =

6

>> y = 7; …what happens when you type this?

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Pythagoras' Theorem: Hypotenuse2 = Height2 + Base2

1. Create a script file and name it Pyth.m

2. Clear the command window

3. Clear all variables from memory

4. Display your name and seat number

5. Declare height of triangle as 3 units

6. Declare base of triangle as 4 units

7. Find the hypotenuse of the triangle

Height

Base

Hypotenuse

Script File Example

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How To Turn In All Assignments

You must print two things for every MATLAB assignment:

1. Script file 2. Command window output

… if you do not turn in both, you will lose points

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Example Script File Printout

Example Command Window Printout

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• Arithmetic Operations with scalars: 5+3, 5*3 , 5^3

• Precedence of operations: 7+8/2 vs. (7+8)/2 • Variable assignment: a=8, b=12• Calculations with variables: a+b, a*b• Important commands: clc, clear• Use of semi colons (;) to suppress output• Display function: disp(‘Brutus Buckeye’)• Mathematical functions: sin(pi/2) , exp(2) • Calculate the value of (cos2xsinx + tan(x/2)) /

exp(3x) for x = 30 degrees

Self Check… Do you understand these concepts?

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Homework Assignment

MAT-01Introduction to Matlab