MEEN 2240

PROGRAMMING FOR
MECHANICAL ENGINEERS

Instructor: Dr. Yunwei Xu

Dept of Mechanical Engineering
University of North Texas
Chapter 1
Introduction to MATLAB

i. The MATLAB Desktop Environment (s5-s6)

ii. Variables and Assignment Statement (s7-s9)

iii. Type ranges and Type Casting (s10-s12)

iv. Numerical Expressions (s13-s14)

v. Formatting (s15)

vi. Built-in Numerical Functions & Math Operators (s16-s23)

Copyright © 2020 Yunwei Xu, PhD 2

MATLAB Functions
and Commands
MATLAB
Operators

Copyright © 2020 Yunwei Xu, PhD 3

 Introduction

• Very powerful software package

• Many mathematical and graphical applications

• Has programming constructs

• Also has many built-in functions

• Can use interactively in the Command Window, or write

your own programs

Copyright © 2020 Yunwei Xu, PhD 4

 MATLAB Installation and Textbook Requirement

• Click on the link below and enter your UNT email ID (.@my.unt.edu)
https://www.mathworks.com/academia/tah-support-program/eligibility.html

• You will receive email for creation of MathWorks account. Enter your credentials and
follow the instructions for downloading and activating the software.

• Kindly let me know if you have any questions.

• MATLAB – A Practical Introduction to Programming and Problem Solving, 5th Edition,

Elsevier, 2018
Stormy Attaway
ISBN-13: 978-0128154793

Copyright © 2020 Yunwei Xu, PhD 5

 MATLAB Desktop Environment
Working Directory:
shows location where you are currently
working. Files will be saved here.

Command Window: Workspace:

Current Folder:
can use for simple shows information of all
shows files in current
calculations, to run variables
working directory
programs, access help
menu, etc. Command History:
shows recent commands
entered in the command
window

Copyright © 2020 Yunwei Xu, PhD 6

 MATLAB Desktop Environment

Layout: Arrange the windows and positioning by going to here Preference: MATLAB appearance can be changed
on the toolbar by going here, for instance:
• Colors – to change the background and font
colors
• Fonts – to modify font type and size

Copyright © 2020 Yunwei Xu, PhD 7

 Variables and Assignment Statement
• variables: to store values
• one way to put a value in a variable is with an assignment statement
• general form:
variable = expression
• The order is important
• variable name on the left
• the assignment operator “=” (Note: this does NOT mean equality)
• expression on the right

Copyright © 2020 Yunwei Xu, PhD 8

 Variables and Assignment Statement

Example 1:

i. The value 3 is assigned to the

variable mynumber.

ii. mynumber is changed to have

the value of the expression 4+2
(or 6).

iii. mynumber is changed to 6+1 (or

7).

iv. Semi-colon (;) to prevent this

repetition, no result is shown.

Note: MATLAB goes from top to

v. but double-chick “mynumber” in Workspace, result can be found under the
bottom when doing calculations
variable (MATLAB only stores/uses the last calculated value).

Copyright © 2020 Yunwei Xu, PhD 9

 Variables Names
 Names must begin with a letter of the alphabet

 After that names can contain letters, digits, and the underscore character _

 MATLAB is case-sensitive:

mynum ≠ MYNUM ≠ Mynum

 Use informative names

• Names should make sense!
• Generic names like abc or number are difficult to remember
• Think about writing a code and then coming back to it

three months from now… will you remember what the

variables are?
If not, rename them!
 clearvars: to delete all variables

 clear: to delete all variables and functions

 clc: clears out variables and also commends

 The commands who and whos will show variables

Copyright © 2020 Yunwei Xu, PhD 10

 Types or Class
 Every expression and variable has an associated type, or class

 Real numbers: single, double

 The default type for numbers is double

 Integer types: numbers in the names are the number of bits used to store a value of that

type

 Signed integers (store sign and integer): int8, int16, int32, int64

 Unsigned integers (only store integer, integer can only be positive): uint8, uint16,
uint32, uint64

 Single characters and character vectors: char (e.g., ‘abc’)

 Strings of characters: string (e.g., “hello”)

 True (1)/false (0): logical

 Show all variables: who and whos

Copyright © 2020 Yunwei Xu, PhD 11

 Types or Class

Binary system
only store 0s or 1s
Decimal system

Int 8

0 0 0 0 0 1 0 0 =4
Sign Value
bit bits

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 Type Casting

• Need to switch from a

double(double precision) to an
integer?
• Use type casting!
• Use the type names to switch from
one to the other

Example 2:

Having a variable num equal to 2.6

(with double precision), want to
convert 2.6 to an 8-bit integer?

Type casting converts num to an

integer with a value of 3.

Copyright © 2020 Yunwei Xu, PhD 13

 Numerical Expressions

 Expressions can contain:

values
variables (that have already been initialized before being used)
operators
built-in functions
parentheses

 Operators include:
+ addition
- negation, subtraction
* multiplication
/ division (divided by e.g. 10/5 is 2)
\ division (divided into e.g. 5\10 is 2)
^ exponentiation (e.g. 5^2 is 25)

 Scientific or exponential notation:

use e for exponent of 10 raised to a power
 e.g. 3e5 means 3 * 10^5

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 Operator Precedence

 Similar with algebra, operators within MATLAB have precedence over

others

 Precedence list (highest to lowest) so far:

() parentheses

^ exponentiation

- negation

*, /, \ all multiplication and division

+, - addition and subtraction

 Nested parentheses: expressions in inner parentheses are evaluated first

 Be careful when creating long expressions

Copyright © 2020 Yunwei Xu, PhD 15

 Formatting
• format changes how values are displayed:

• short – 4 digits to right of decimal

• long – 15 digits to right of decimal

• longg (take out scientific notation)

• Scientific or exponential notation:

• use e

• Example: 8e7 equates to 8 * 107

• Have a long expression?

• use the ellipsis (…)

• allows all code to be seen without scrolling to
the right

• Other format options:

• Type: help format

Copyright © 2020 Yunwei Xu, PhD 16

 Built-in Numerical Functions
 There are large number of built-in functions in
MATLAB
 Built-in functions allow the user to complete a
range of tasks quickly and easily
 There are functions that perform simple
calculations
 such as: sin (radian), cos, sind (degree),
abs, plus
 There are functions that perform complex
calculations
 such as a numerical integration or
curve fitting
 To see a list of help topics, type “help” at the
prompt:
>> help
 To find out about a particular function, e.g. sin:
>> help sin

Copyright © 2020 Yunwei Xu, PhD 17

 Using Numerical Functions

 To use a function, you call it

 To call a function, give its name followed by the argument(s) that are passed to it in
parentheses

 Many functions calculate values and return the results

 For example, to find the absolute value of -5

argument

function name
returns result

 The name of the function is “abs”

 One argument, -5, is passed to the abs function

 The abs function finds the absolute value of -5 and returns the result, 5

Copyright © 2020 Yunwei Xu, PhD 18

 Numerical Functions
• Trig functions:
• sin, cos, tan, sec, csc, cot
• Arguments must be in radians
• sind, cosd, tand, secd, cscd, cotd
• Arguments must be in degree
• Arc functions: asin, acos, atan, asec, acsc, acot
• Returns angle in radians
• Exponential functions:
• exp – exponential
• exp (-2) equates to e −2
• log – natural log
• log (1) equates to ln 1
• sqrt – square root
• sqrt (4) equates to 4

Copyright © 2020 Yunwei Xu, PhD 19

 Numerical Functions

• Random Numbers
• call rand – generate one random real number in the open interval (0,1)
• call randi(imax) to generates a random integer in the range from 1 to imax
• how to generate one random real number within (0, 10)?

Copyright © 2020 Yunwei Xu, PhD 20

 Numerical Functions

• Complex functions:
• conj: complex conjugate
• imag: complex imaginary part
• real: complex real part
• Rounding functions:
• round: round towards nearest integer
• ceil: rounds up towards +∞
• floor: rounds down towards −∞
• fix: rounds towards zero
• sign: gives + or -

Copyright © 2020 Yunwei Xu, PhD 21

 Characters and Strings
 A character is a single character in
single quotes: ‘ ’
 All characters in the computer’s
character set are put in an order
using a character encoding
 In the character encoding
sequence, the letters of the
alphabet are in order, e.g. ‘a’
comes before ‘b’
 Common encoding ASCII has
128 characters, but MATLAB
can use a much larger encoding
sequence
 The character set includes all letters
of the alphabet, digits, punctuation
marks, space, return, etc.
 Character vectors are sequences of
characters in single quotes, e.g.
‘abc’
 Strings are sequences of characters
in double quotes: “ ”, e.g. “hello”
Copyright © 2020 Yunwei Xu, PhD 22
 Logical – Relational Expressions
 The relational operators in MATLAB are:

> greater than

< less than

>= greater than or equals

<= less than or equals

== equality

~= inequality

 The resulting type is logical, 1 for true or 0 for false

 The logical operators are:

|| or for scalars

&& and for scalars

~ not

 Also, xor function which returns logical true if only one of the arguments is true

Copyright © 2020 Yunwei Xu, PhD 23

 Constants

• Constant – known value that does not change

• MATLAB has built-in constants

• pi: 𝜋

• i or j: −1

• Inf ,-Inf: 
• NaN: not a number
• You don’t want to see this!
• Means your tried to divide by zero.

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 Getting Help

• To see a list of help topics,

use the command help
>> help

• To find out about a particular

function like absolute value:
>> help abs

Copyright © 2020 Yunwei Xu, PhD 25

 Practices
Example 3: Example 4:

Calculate the area moment of inertia for Determine the final displacement after
circular area as below, with the radius 20 seconds of a car that has an initial
(r) is 2 m. velocity of 40 m/s and a deceleration of
1 1m/s2. Initial displacement is 300 m.
Ix =  r4
4 The kinematic equation is:

1
s = s0 + v0t + at 2
2

Change to short format

Copyright © 2020 Yunwei Xu, PhD 26

 Practices
Example 5: Example 6:
Calculate the cosine of 60⁰. Test out the various rounding function for π.

Method 1: calling the function cosd

and 60 is the input argument.

Method 2: calling the function cos,

but convert 60 degrees into radians,
to be the input argument.

Copyright © 2020 Yunwei Xu, PhD 27

 Quiz 1
1. To install MATLAB on your laptop.

2. The combined resistance RT of three resistors R1, R2, and R3 in parallel is given by
1
RT =
1 1 1
+ +
R1 R2 R3
Determine the RT if
R1 = 45 
R2 = 55 
R3 = 65 
round your result towards nearest integer.

3. In special relativity, the Lorenta factor is a number that describes the effect of speed on various physical
properties when the speed is significant relative to the speed of light. Mathematically, the Lorentz factor is given
as: 1
=
v2
1−
c2

Use 3 × 108 m/s for the speed of light, c. Create variable for c and the speed v and from them a variable lorentz for
the Lorentz factor. Determine the Lorentz factor if the speed v = 50 m/s.

4. Use the deg2rad function to convert 90 degrees to radians.

Copyright © 2020 Yunwei Xu, PhD 28