matlab lecture 1w03

8/14/2019 Matlab Lecture 1w03

1/22

MATLAB - Lecture # 1

Topics Covered:

1. Introduction.

2. MATLAB windows.

3. Arithmetic operations with scalars.

4. Working in the command window.

5. Defining variables (scalars).

Starting with MATLAB / Chapter 1


2/22

MATLAB is a software for numerical computations,

visualization and programming.The name MATLAB stands forMATrix LABoratory.

Its basic data element is an array (explained later).

With MATLAB you can:

Use it as a calculator.

Define variables and use them in calculations.

Use built-in functions (sin, cos,max,min, etc.).

Plot graphs.

Write and run computer programs.

Do symbolic calculations.

1-4


3/22

Command Window: Main window that opens whenMATLAB is started. It has the command prompt .

All commands can be typed in this window. Used for

running programs written by user.

Figure Window: Contains graphs created by graphics

commands. This window opens automatically.

Editor Window: Used for writing and editing

programs. This window is opened from the File menuin the Command Window.

Help Window: Contains help information. This

window is opened from the Help menu in any of the

previous windows.

MATLAB windows:6


4/22

Command Window(The Command Window opens

when MATLAB is started)

Command prompt

6


5/22

Figure Window (The Figure Window opensautomatically by the plot command)

7


6/22

(The Editor Window is opened from the

file menu in the Command Window)Editor Window

7


7/22

Help Window (The Help Window can be opened from theHelp menu of any of MATLAB windows)

8


8/22

WORKING IN THE COMMAND WINDOW

To type a command the cursor must be placed

after the command prompt (>>). Once a command is typed, and the Enter key is

pressed, the command is executed. (Only the last

command is executed. Everything executed before

is unchanged) It is not possible to go back to a previous line and

make a correction.

A previously typed command can be recalled tothe command prompt with the up-arrow key .( )

8-9


9/22

ARITHMETIC OPERATIONS WITH SCALARS

NOTE: For scalars the arithmetic operations are the usual

ones. For vectors and matrices the arithmetic operations can

either follows matrix algebra rules, or can be performed on

element-by-element basis (discussed in the next lectures).

10

Operation Symbol Example

Addition + 5+3

Subtraction - 5-3

Multiplication * 5*3

Right Division / 5/3

Left Division \ 5\3=3/5

Exponentiation ^ 5^3


10/22

ORDER Of PRECEDENCE

(The order in which operations are executed by the computer)

Higher-precedence operations are executed before lower-precedence operations.

If two operations have the same precedence, then the expression is

executed from left to right.

PRECEDENCE OPERATION

First Parentheses, starting with the innermost pair.

Second Exponentiation.

Third Multiplication and division (equal precedence).

Fourth Addition and subtraction (equal precedence).

10


11/22

Using numbers:

8/2 is executed first

7+8 is executed first

5/3 is executed first

USING MATLAB AS A CALCULATOR

>> 7+8/2

ans =

11

>> (7+8)/2ans =

7.5000

>> 4+5/3+2

ans =

7.6667

Type and press Enter

Computer response


Computer response


Computer response

11


12/22

5^3 is executed first,

/2 is executed next.

1/3 is executed first,

^ is executed next,

+ is executed last.

27^1 and 32^0.2 is

executed first,

/3 is executed next,+ is executed last.

5^3/2

ans =

62.5000>>

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

ans =

5

>> 27^1/3+32^0.2

ans =

11


Computer response


Computer response


Computer response

11

12


13/22

DISPLAY FORMATS

12-13

The format command controls how output numbers appear on the

screen. Input numbers can be written in any format.

format short (the default) 41.4286 Fixed-point with 4 decimal

digits.

format long 41.42857142857143 Fixed-point with 14 decimal

digits.

format short e 4.1429e+001 Scientific notation with 4

decimal digits.

format long e 4.142857142857143e+001 Scientific notation with

15 decimal digits.

Format bank 41.43 Two decimal digits.

MATLAB has several other formats in which numbers can be displayed.

13


14/22

MATLAB BUILT-IN MATH FUNCTIONS

In addition to arithmetic operations, MATLAB can be used to

calculate elementary math functions. The most common ones are:

Examples:

>>

sin(0.78539)

ans =

0.7071

>> sqrt(169)

ans =

13

>> log10(10000)

ans =

4

MATLAB has hundreds of built-in functions (this will be discussed in

future lectures).

13-15

sin(x) x in radians

cos(x) x in radians

tan(x) x in radians

cot(x) x in radiansThe inverse is: asin(x),

acos(x), etc.

exp(x) exponential

log(x) natural logarithm

log10(x) base 10 logarithm

sqrt(x) square rootabs(x) absolute value

16


15/22

THE ASSIGNMENT OPERATOR

Variable = A value, or a computable value

The left

hand side

can only beonevariable.

The right hand side can be a

specific value, or a computable

expression (an expression thatincludes values and/or previously

defined variables).

16-18

In MATLAB, the = sign is called the ASSIGNMENT

OPERATOR.

The ASSIGNMENT OPERATOR assigns a value to a variable.

16


16/22

THE ASSIGNMENT OPERATOR

For example, if you type:

>> x = 3

x =

3

MATLAB assigns a new value to x, whichis the old value 3 plus 5.

(In mathematics this expression has no

meaning since it implies: 0 = 5.)

MATLAB assigns the value of 3 to x.

If then you type:

>> x = x +5

x =

8

For example, the statement:

x + 4 = 30 is not valid. MATLAB does not solve for x,

but the statement:

x = 30 4 is valid (the number 26 is assigned to x.)

16-18

16


17/22

DEFINING VARIABLES

A variable is defined by typing a variable name followed by the

assignment operator (equal sign) and then a value, or a

mathematical expression.

Once a variable is defined, the computer remembers and stores its

value. The variable can then be used in further calculations.

>> a=8

a =

8

>> B=12

B =

12

>> a+B

ans =

20

>> a/B

ans =

0.6667

>> B/a

ans =

1.5000

>> B^a

ans =

429981696


Computer response


Computer response

16-18

16


18/22

Variables can also be used to define new variables

Once in existence, variables can be used in functions

>> d=a*B

d =

96

>> sqrt(d)

ans =

9.7980

A previously defined variable can be redefined and reassigned

a new value.

16-18


19/22

RULES ABOUT VARIABLES NAMES

Variable names can be up to 63 characters long.

Variable name can contain letters, digits, and

the underscore character.

Variable name must begin with a letter.

MATLAB is case sensitive; it distinguishes

between uppercase and lowercase letters. For

example,Aand a are not the same variable.

18


20/22

18


21/22

PREDEFINED VARIABLES

>> pi

ans =

3.1416

Typing these variables gives:

>> eps

ans =

2.2204e-016

>> inf

ans =

Inf

>> i

ans =

0 + 1.0000i

>> sin(pi/4)

ans =

0.7071

18-19

MATLAB has several variables that are predefined.

These variables can be redefined to have any other value.It is probably better not to use the predefined variables as

variable names.

Some of the predefined variables are:

pi ( ), eps (the smallest difference between two numbers)

inf (infinity)

i (square root of 1) j (square root of 1)

ans (the value of the most recent calculation)


22/22

matlab lecture 1w03

Documents