GNU octave

CONTENTS
 Introduction
 History
 Issues of matlab users
 Technical Details
 Some useful OCTAVE commands
 Introduction to Matrix
 Array , Vector and Matrix
 Plotting
 Functions
 Scripts
 Difference between Matlab And Octave

INTRODUCTION
 High level programming language
 Open Source Implementation
 Available in Linux and Windows
 Distributed in GPL(Gnu Public License)
 Designed for matrix computations

HISTORY
The project was conceived around 1988 . At first it was
intended to be a companion to a chemical reactor design
course. Real development was started by John W. Eaton in
1992. The first alpha release dates back to January 4, 1993 and
on February 17, 1994 version 1.0 was released. Version 4.0.0
was released on May 29, 2015. The latest version 5.1.0 of GNU
octave was released on March 1,2019.

ISSUES FOR MATLAB USERS
Licensing – Octave is free
Multi-processor and cluster
64-bit systems and large memory (> 2GB)
Lack of GUI support
Compatibility/portability issues with other analysis packages (e.g., R)
Speed (we need to convert more .m files to C++)

TECHNICAL DETAILS
 Written in C++ using the C++ standard library.
 Uses an interpreter to execute the Octave scripting language.
 Octave interpreter has an OpenGL-based graphics engine to create
plots, graphs and charts and to save or print them.
 Octave includes a Graphical User Interface (GUI) in addition to the
traditional Command Line Interface (CLI).

SOME USEFUL OCTAVE COMMANDS
 who List Known variables
 whos List known variables plus their size
 help help in finding any command
 clear Clear all variables from workspace
 clear x y Clear variables x and y from workspace
 clc Clear the command windows
 ver Display the information of version of OCTAVE
 exit quit from OCTAVE session

INTRODUCTION TO MATRIX
Creating a Matrix
Simply type:
octave:1> A = [8, 2, 1; 3, -1, 4; 7, 6, -5]
Octave will respond with a matrix in pretty-print:
A =
8 2 1
3 -1 4
7 6 -5

Indexing
Always "row before column"!
aij = A(i,j) Get an element
r = A(i,:) Get a row
c = A(:,j) Get a column
B = A(i:k,j:l) Get a submatrix
Useful indexing command end :
octave:1> data = [4 -1 35 9 11 -2];
octave:2> v = data(3:end) ;
v =
35 9 11 -2

ARRAYS, VECTORS, AND MATRICES
Array :
A collection of data elements
arranged in rows and columns
C={1 , 2 , 3; 4 , 5 , 6};
Vector:
A one-dimensional array (single row or
single column of data elements)
Matrix :
A two-dimensional array (more than
one row and/or column of data
elements)
>> A=[1;9]
>> B=[1;8;3;7]
>> C=[1:3; 4:6; 7:9]
row or column?
column vector
C =
1 2 3
4 5 6
7 8 9

PLOTTING
Plotting in 2D
 plot(x,cos(x)) Display x,y-plot
Creates automatically a figure window. Octave uses gnu plot to
handle graphics.
 figure(n) Create figure window 'n'
If the figure window already exists, brings it into the foreground
(makes it the current figure)
 figure Create new figure window with
identifier incremented by 1

EXAMPLE OF PLOTTING
>> x=0:pi/100:2*pi;
>> y1=sin(2*x);
>> y2=2*cos(2*x);
>>plot(x,y1);
>> hold on;
>> plot(x,y2);

FREQUENT COMMANDS
▪ clf Clear figure
▪ hold on Hold axes. Don't replace plot with
new plot, superimpose plots
▪ grid on Add grid lines
▪ grid off Remove grid lines
▪ title('Exp1') Set title of figure window
▪ xlabel(‘label name ') Set label of x-axis
▪ ylabel(‘label name') Set label of y-axis
▪ subplot Put several plot axes into figure

LINE SPECIFIERS
Line Style Specifier
Solid(Default) -
Dashed --
Dotted .
Dash-dot -.
Line color Specifier
Red r
Green g
Blue b
Cyan c
Magenta m
Yellow y
Black k
White w

Ex : Find the response to an input of 5u(t).
Given that amplitude of step input is 5 .
Program:
Sys1=tf([1 1 ]*5,[4 4])
Sys2=tf([1]*5,[4 1])
Step(sys,1);
Hold on;
Step(sys,2)

FUNCTIONS
Functions and their m-File
▪ When putting a function into its m-file, the name of that file must be the
same as the function name plus the .m extension.
Examples: calcmoments.m, findfirstpeak.m
▪ To call a function, type its name without the .m extension. Example:
[bool i] = findfirstpeak(myreadings, 0.3);
▪ Comments in Octave/Matlab start with % .

SCRIPTS
Scripts
▪ The second type of m-files is called script. Again, Octave scripts
are text files with an
.m extension.
▪ Scripts contain executable code. They are basically the "main"
programs.
▪ Execute a script by typing its name without the .m extension!
Example: octave:1> LocalizeRobot

DIFFERENCE BETWEEN MATLAB AND
OCTAVE
The Basic Comparison
between Matlab vs Octave
Matlab Octave
Definition It is a matrix laboratory, referred
to as language used for technical
computing.
It is programming language used
for numerical computing.
Programmed It was written in C, C++ and Java
programming language.
It was written in C, C++ and
Fortran Language.
Interface It has better interface
comparatively.
Its interface is not that good as
MATLAB is having.
RAM It consumes more RAM as
compared to Octave.
It consumes less RAM than
MATLAB.
Free It is not free It is free

GNU octave

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