MATLAB BASICS

Variables

No need for types. i.e.,

All variables are created with double precision unless specified and they are matrices.

After these statements, the variables are 1×1 matrices with double precision

Array, Matrix

  • a vector x = [1 2 5 1]
x =
      1   2   5   1
  • a matrix x = [1 2 3; 5 1 4; 3 2 -1]
x =
   1     2     3
   5     1     4
   3     2    -1

transpose y = x’

y =
1
2
5
1

Long Array, Matrix

t =1:10 
t =
      1   2   3   4  5  6   7  8   9   10


k = 2:-0.5:-1 
k =
      2  1.5  1  0.5  0  -0.5  -1


B = [1:4; 5:8]
B =
   1     2     3    4
   5     6     7    8

Generating Vectors from functions

  • zeros(M,N) :: MxN matrix of zeros

x = zeros(1,3)
x = 0 0 0

  • ones(M,N) :: MxN matrix of ones

x = ones(1,3)
x = 1 1 1

  • rand(M,N) MxN matrix of uniformly distributed random numbers on (0,1)

x = rand(1,3)
x = [0.9501 0.2311 0.6068]

Matrix Index

The matrix indices begin from 1 (not 0 (as in C))
The matrix indices must be positive integer

Given:

A(-2), A(0)
Error: ??? Subscript indices must either be real positive integers or logicals.
A(4,2)

Error: ??? Index exceeds matrix dimensions.

Concatenation of Matrices

x = [1 2], y = [4 5], z=[ 0 0]

A = [ x y]

      1   2   4   5

B = [x ; y]

    1 2
    4 5

C = [x y ;z]
Error:
??? Error using ==> vertcat CAT arguments dimensions are not consistent.

Operators (arithmetic)

+ addition

– subtraction

* multiplication
division
^ power
‘ complex conjugate transpose

Matrices Operations

Operators (Element by Element)

.* element-by-element multiplication
./ element-by-element division
.^ element-by-element power

The use of “.” – “Element” Operation

K= x^2
Erorr:
??? Error using ==> mpower Matrix must be square.
B=x*y
Erorr:
??? Error using ==> mtimes Inner matrix dimensions must agree.

Basic Task: Plot the function sin(x) between 0≤x≤4π

Create an x-array of 100 samples between 0 and 4π.

Calculate sin(.) of the x-array

Plot the y-array

Plot the function e-x/3sin(x) between 0≤x≤4π

Create an x-array of 100 samples between 0 and 4π.

Calculate sin(.) of the x-array

Calculate e-x/3 of the x-array

Multiply the arrays y and y1

Plot the function e-x/3sin(x) between 0≤x≤4π

Multiply the arrays y and y1 correctly

Plot the y2-array

Display Facilities

  • plot(.)
  • stem(.)
  • title(.)
  • xlabel(.)
  • ylabel(.)

Operators (relational, logical)

== Equal to
~= Not equal to
< Strictly smaller
Strictly greater
<= Smaller than or equal to
= Greater than equal to
& And operator
| Or operator

Flow Control

if
for
while
break
….

Control Structures

  • If Statement Syntax
if (Condition_1)
		Matlab Commands
elseif (Condition_2)
		Matlab Commands
elseif (Condition_3)
		Matlab Commands
else
		Matlab Commands
end


Some Dummy Examples

if ((a>3) & (b==5))
     Some Matlab Commands;	
end

if (a<3)
     Some Matlab Commands;
elseif (b~=5) 
     Some Matlab Commands;
end

if (a<3)
     Some Matlab Commands;
else     
     Some Matlab Commands;
end

  • For loop syntax
for i=Index_Array
	Matlab Commands
end

Some Dummy Examples

for i=1:100
     Some Matlab Commands;
end

for j=1:3:200
     Some Matlab Commands;
end

for m=13:-0.2:-21
     Some Matlab Commands;
end 

for k=[0.1 0.3 -13 12 7 -9.3]
     Some Matlab Commands;
end

  • While Loop Syntax
while (condition)
	Matlab Commands
end

Dummy Example

while  ((a>3) & (b==5))
     Some Matlab Commands;	
end


Use of M-File

  • Extension “.m”
  • A text file containing script or function or program to run

Writing User Defined Function

  • Functions are m-files which can be executed by specifying some inputs and supply some desired outputs.
  • The code telling the Matlab that an m-file is actually a function is
  • You should write this command at the beginning of the m-file and you should save the m-file with a file name same as the function name
  • Examples
  • Write a function : out=squarer (A, ind)
  • Which takes the square of the input matrix if the input indicator is equal to 1
  • And takes the element by element square of the input matrix if the input indicator is equal to 2
  • Another function which takes an input array and returns the sum and product of its elements as outputs
  • The function sumprod(.) can be called from command window or an m-file as

Notes:

  • “%” is the neglect sign for Matlab (equaivalent of “//” in C). Anything after it on the same line is neglected by Matlab compiler.
  • Sometimes slowing down the execution is done deliberately for observation purposes. You can use the command “pause” for this purpose

Useful Commands

The two commands used most by Matlab users are

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