MATLAB Octave CLI

Internal

• MATLAB/Octave
• MATLAB/Octave Concepts

Overview

';' after a statement suppressed the default output to stdout.

Comments

% this is a comment

Prompt

PS1('>> ')

Search Path

addpath('<directory-name>')

Script Execution

Scripts from the current directory are executing by specifying the name of the script (without the .m extension). To update the current directory use cd.

In-Line Operations

1 + 2
2 - 1
1 * 2, 2 * C % where C is a matrix
2 / 1
2 ^ 6 

Logical operations

Equality:

1 == 2

Non-equality:

1 ~= 2

Logical AND:

1 && 0

Logical OR:

1 || 0

Variable Assignment

Also see:

Variables

Scalar Variable Assignment

<scalar-variable-name> = <variable-value>

Vector Variable Assignment

Vector indices are 1-based.

Vector

Assignment and literal initialization:

<vector-variable-name> = [ v1 v2 v3 ... ] % An (1, n) vector
<vector-variable-name> = [ v1; v2; v3; ... ] % An (n, 1) vector

Other Types of Vector Initialization

Start from "start-value" (inclusively), increment with "increment-step" until the value is strictly larger than "end-value":

v = <start-value>:<increment-step>:<end-value>

Start from "start-value" to "end:value" with increments of 1:

v = <start-value>:<end-value>

v = zeros(1, 3)
v = zeros(3, 1)
v = ones(1, 3)
v = ones(3, 1)

Matrix Variable Assignment

Matrix indices are 1-based.

Matrix

Assignment and literal initialization:

<two-dimensional-matrix-variable-name> = [ v11 v12 ... v1n;  v21 v22 ... v2n; ...; vm1 vm2 ... vmn ] % A (m, n) matrix.

Example:

A = [1 2; 3 4]

Commas between row elements are accepted and ignored:

A = [1, 2; 3, 4]

Other Types of Matrix Initialization

C = zeros(2, 3)
C = ones(2, 3)

Concatenation

A = ...
B = ...
C = [A B] % same as [A, B]
C = [A; B]

Data Selection

Indexing

An element of a matrix:

<Matrix-var-name>(<1-based-row-number><1-based-column-number>)

A(2, 3)

Subset Indexing

These indexing mechanism can be used to access data, but also to assign data in the original variable, by specifying the selection expression at the left of the assignment.

Vector Indexing

Subset of a vector:

v(<first-index>:<last-index>)

Matrix Indexing

Everything in a second row of a matrix:

A(2, :)

Everything from the first and the third row:

A([1 3], :)

Everything in the second column:

A(:, 2)

Everything in the first and the second column:

A(:, [1, 2])

All Elements of Matrix in a Single Column Vector

A(:)

Variable Management

who

Shows the name of the variable in the work space.

whos

Details about variables in the work space.

clear

Delete the names matching the pattern from the symbol table. The pattern is a simplified regular expression, with '?', '*', '[...]'. With no arguments, all user-define variables (local and global) are deleted.

Initialization Functions

zeros

v = zeros(1, 3)
C = zeros(2, 3)

ones

v = ones(1, 3)
C = ones(2, 3)

eye

Returns an identity matrix. When invoked with a single scalar argument n, it returns a square n x n identity matrix.

C = eye(3)

rand

v = rand(1, 3)
C = rand(2, 3)

randn

Gaussian.

v = randn(1, 3)
C = randn(2, 3)

Data Size

size

size()

Dimensions of a matrix:

size(A)

Returns a vector with two elements (number of rows and number of columns).

Number of rows of a matrix:

size(A, 1)

Number of columns of a matrix:

size(A, 2)

length

Should only be applied to vectors, for matrices is confusing.

numel

Return the number of elements in the object A. Optionally, if indices i1, i2, ... are supplied, return the number of elements that would result from indexing with the given indices.

numel(A)

Element-Wise Operations

Element-wise multiplication

A .* B

Element-wise comparison:

A < 3

Other element-wise operations:

A .^ 2

1 ./ A

Transpose

A'

Inverse

inv(A)

Pseudo-inverse:

pinv(A)

Data Loading and Saving

load

Load the named variables from the file. If no variables are named, all variables found in the file will be loaded. Note that the file is in ASCII format, no variable names are saved in the file, so the variable that will be created will be named after the file (the basename of the file name).

load <file-name>

load('<file-name>')

data = load('<file-name>')

save

save <file-name.mat> <variable-name>

Saves the data in a MATLAB format, and the variable name is also saved in the file.

To save the data as ASCII (the name of the variable is not saved in the file):

save <file-name.txt> <variable-name> -ascii

Display

By default, the runtime displays 5 significant digits in human readable format (format short for scalars and format loose for matrices).

To print the value of the variable, simply type the name of the variable:

<variable-name>

disp

disp(<variable-name>)

Also see format.

printf

printf
fprintf
sprintf

a = pi;
sprintf('this is pi with 6 decimals %0.6f', a);

fprintf() is like printf(), just that the output is written to the FID stream instead of stdout.

Also see:

Generic printf

format

Reset or specify the format of the output produced by disp and the normal output mechanism.

Also see:

Display

short

Fixed point format with 5 significant figures in a field that is a maximum of 10 characters wide.

Control Elements

Loops

For all loops, 'break' and 'continue' work:

for

for i = <range> <statement> end;

for i = 1:10 disp(i) end;

The range can be a vector:

v = [2 4 6 8]
for i = v disp(i) end;

while

i = 1;
while i <= 5; i = i + 1; end;

if

if <condition> 
    <statement> 
endif;

if <condition> 
    <statement> 
else 
    <statement> 
endif;

if <condition> 
    <statement> 
elseif <condition>
    <statement> 
...
else 
     <statement> 
endif;

Functions

Create a file with a .m extension and a content similar to:

function [return-variables =] <function-name>([comma-separated arguments])
<body>
end

The "return-variables" section of the function header defines which variables represent the return values of the function. A function may return zero, one or more values.

A function that does not return a value:

function somefunc(...)

A function that returns one value:

function result = somefunc(...)

A function that returns multiple values:

function [result1, result2] = somefunc(...)

A function may have zero, one or more arguments. The () must be specified even if there are no arguments.

The function body uses the arguments and assigns values to the return variables defined in the function header.

Input

fprintf('Program paused. Press enter to continue.\n');
pause;

Filesystem

cd

Modify the current directory.

pwd

Print working directory.

Miscellaneous

clc

Clears the terminal screen and move the cursor to the upper left corner.

max

max(A) does column-wise maximum for a matrix.

max(A, [], 1)
max(A, [], 2)

Maximum for the entire matrix:

max(max(A)) 

Equivalent with

max(A(:))

sum

Fun of all elements along the specified dimension.

For a vector sums all elements.

For a matrix, sums columns and presents the result as a horizontal vector.

Plotting

figure

Opens a new (empty) figure window. It can be closed with close.

plot

Displays a 2D plot. Several invocation styles are available:

Display Y Values Evenly Spaced

plot(y[, property, value, ...])

This is equivalent with:

plot(1:numel(y), y)

Display x,y Pairs

plot(x, y, 'rx', 'markersize', 10);

Format arguments:

• marker color ('r', 'g', 'b', ...)
• maker style ('x', 'o', ....)

Other format properties:

• 'linestyle'
• 'linewidth',
• 'color',
• 'marker'
• 'markersize'
• 'markeredgecolor'
• 'markerfacecolor'

xlabel

Sets the X axis label.

ylabel

Sets the Y axis label.

close

Close figure windows.

Recipes

Average value for a vector: