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MATLAB PRIMER

Energy Engineering Class

College of Engineering

UP Diliman

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Matlab Introduction

MAT(rix) LAB(oratory)

a high-level technical computing language and interactive

environment for algorithm development, data

visualization, data analysis, and numeric computation

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Matlab Interface

Editor Workspace

Command

History

Current

Directory

Command Window

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Matlab Interface

Current Directoryshow the working directory and files

inside the directory

Editor - text-editor where a user can create Matlab (*.m)

m-files

Command Windowwhere a user can issue and call

matlab commands at the prompt

Workspaceshows the current variables and data loaded

into the matlab memory

Command Historyshows a list of previously called or

issued commands

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Creating Variables

Matlab variables can accept any data at creation

No need to declare data type

Example (try it!)

A = 1 B = Hello World

C = [0 1 2 3]

To suppress displaying of data, use semi-colon ( ; ) A = 1;

B = Hello World!

C = [0 1 2 3]

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Creating Matrices

1-dimensional matrix (row vector)

A = [1 2 3 4 5]

Use semicolon to separate data to rows B = [1 2 3; 4 5 6; 7 8 9]

Other special matrices

ones(m,n)

Zeros(m, n)

Rand(m, n)

m = number of rows

n = number of columns

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Matrix Operations

Try it! : Create a 3x3 Matrix C of ones!

Adding matrices B + C

Ans:

2 3 4

5 6 7

8 9 10

TIP: Make sure B and C has the same size

Details the same with subtracting matrices (BC)

To transpose matrices, use a quote ( ) Try it! Make Matrix A a column vector

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Matrix Operations

Matrix Multiplication

Inner products between row and columns

( * )operator

Example

B * B

30 36 42

66 81 96

102 126 150

B * inv(B) inv(B) gets the inverse of the matrix

2 0 2

8 0 0

16 0 8

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Matrix Operations

Element-wise multipication

( .* )dot-asterisk operation

Example

B .* B

1 4 9 16 25 36

49 64 81

Raising Matrix to n-th power (element-wise): B .^ n

B .^ 3 1 8 27

64 125 216

343 512 729

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Matrix Operations

Matrix Division

( / ) or matrix right division: B / A = B * inv(A)

( \ ) or matrix left division: A \ B = inv(A) * B

( ./ ) or array right division: A./B = A/B (element-wise)

( .\ ) or array left division: A.\B = B/A (element-wise)

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Matrix Operation

Concatenation [B, B]

1 2 3 1 2 3

4 5 6 4 5 6

7 8 9 7 8 9

To concatenate vertically, use semicolon instead of coma [B; B]

1 2 3

4 5 6 7 8 9

1 2 3

4 5 6

7 8 9

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Array Indexing

Used to select a part of an array, whether a smaller matrix or acolumn/row vector

A = magic(4) 16 2 3 13

5 11 10 8 9 7 6 12

4 14 15 1

A(4, 2) = ?

A (8) = ?A(1:3, 2) =

2

11

7

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Array Indexing

Try it!

Select and display only the 3rdrow

Select and display the 3rdand 4thcolumn

Select and display the smaller matrix in the 4thquadrant

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Common Matlab functions

Sum

Computes the sum of each column

Try it!

Compute the sum of columns of B

Compute the sum of rows of B

Reshape: Reshapes the matrix into desired new number

of rows and columns

Repmat: Replicates and tiles the input array Str2num / Num2str : converts strings to numbers /vice

versa, respectively

Useful when copying numerical data from external sources

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Importing Data from CSV

To import data from a comma-separated value (CSV)

formatted files, we can use the following functions

M = csvread(filename)

filename- is the name of the CSV file and all data will be read into

variable M

NOTE: data should not have header names (else, error would occur)

M = importdata(filename, delimeter, number_header_lines)

Importdatamore general and flexible compared to csvread

Need not be comma-separated

Delimetercharacter that separates the data (space or comma)

Number_header_lineswhich row data actually starts

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Importing Data from CSV

M = clipboard(pastespecial)

User can open the CSV using a spreadsheet program (MS Excel or

Open/LibreOffice Calc) and copy the data to memory

clipboard will paste these data into Matlab workspace

Data would be separated to texts and numbers

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Display imported data

There are at least 2 ways:

Type the variable name in the Command Window

Would print the values (could be verbose) Double click the variable name in the Workspace window

Variable editor window would open

Variable editor windows shares same space with Editor Window

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Display imported Data

Variable Editor Window

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Plotting Data

To visualize your data, we can use plots

Given a vector of values y, call

plot(y)

The x-axis would be the index of the value

If you have values for the x-axis, call

plot(x,y)

Lets try plotting data!

X = 1:10 Y = rand(10,1) * 10;

Plot the data

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Plotting Data

3-dimensional data For plotting 3-dimensional data, we can use the following

Z = peaks; % lets create 2-dimensional dummy data

surf (To create surface graphs ) surf(Z) surf(X, Y, Z) (if you have value for the X- and Y-axis)

Contour contour(Z)

contour(X, Y, Z) (if you have value for the X- and Y-axis)

surfc (create surface plot and contour plot at the bottom) surfc(Z)

surf(X, Y, Z) (if you have value for the X- and Y-axis)

mesh (similar to surf but retains only the wireframe) mesh(Z)

mesh(X, Y, Z) (if you have value for the X- and Y-axis)

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Control Flow

Control flows are important to direct the execution of your

code depending on the values of your variables

IF, ELSE a = randi(100, 1); % Generate a random number

if rem(a, 2) == 0 % If it is even, divide by 2

disp('a is even')

b = a/2;

else disp('a is odd)

end

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Control Flow

ELSE, ELSEIF

a = randi(100, 1);

if a < 30

disp('small')

elseif a < 80 disp('medium')

else

disp('large')

end

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Control Flow

SWITCH

NOTE: For both IF and SWITCH, once the code enters and executes a

section by satisfying an IF or a CASE, the program exits the code block

Lets Try! Create code by typing a number and telling the user if its a

negative number, a positive number or zero. a = input(Type number: )

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Control Flow

For Loop

Runs a part of the code in a predetermined number of time

H = rand(10);

[m, n] = size(H);

for i = 1:m

for j = 1:n

H(i,j) = 1/(i+j);

end end

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Control Flow

While Loop

Runs the code until a certain condition is met

Code to find the zero of f(x) = x3-2x -5 between 0 and 3

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Control Flow

Continue

Goes to the next iteration of the Loop, skipping all the commands

after it

Code below counts the number of command lines in a Matlab m-

file. It skips counting when a line in the file is not considered a code(either a comment/ %, invalid character or is a whitespace)

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Control Flow

Break

Enables early exit in a loop execution

Code below is similar to the While-Loop but break was utilized

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Control Flow

Return

Break the flow of the program and gives back the control to the

main function, will skip all the succeeding parts of the code.

Usually found at the end of a function to return control to the

invoking function Can also be inserted in middle part of the code to cause premature

exit of execution

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Using (and creating) Functions

Matlab has lots and lots of functions!

You too can create your own

Format:

functionoutput = function_name(input)

output = do_operations_on_(input)

end

Save your file with the *.m extension

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Using (and creating) Functions

Try it!

Implement the factorial (!) as matlab code.

Definition: n! = n * (n-1)!

0! = 1

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Resources

Matlab Primer (www.mathworks.com)

Google is your bestfriend

Matlab File Exchange

Lots of community developed code and software

Forums on Matlab problems and tips

http://www.mathworks.com/http://www.mathworks.com/