Introduction to Scilab 5.3 and Xcos - · PDF fileRunning Scilab From Linux or Windows just...

Introduction to Scilab 5.3 and Xcos
Gianluca Antonelli
Universita degli Studi di [email protected]
http://webuser.unicas.it/lai/roboticahttp://www.docente.unicas.it/gianluca antonelli
Gianluca Antonelli Scilab 5.3
http://webuser.unicas.it/lai/roboticahttp://www.docente.unicas.it/gianluca_antonelli

License
Copyright (c) 2011 GIANLUCA ANTONELLI.Permission is granted to copy, distribute and/or modify this documentunder the terms of the GNU Free Documentation License, Version 1.2 orany later version published by the Free Software Foundation; with noInvariant Sections, no Front-Cover Texts, and no Back-Cover Texts.A copy of the license is available at www.gnu.org

Introduction
The open source platform for numerical computation
Available at http://www.scilab.org

The others
Matlab
Octave
Freemat
Scicoslab
. . .

Running Scilab
From Linux or Windows just selecting the application from theGraphical Menu
From Linux also from the shell typing ./scilab from the correct path

Scilab command line
Scilab command line is denoted with the symbol
-->
It accepts variables declaration, expressions, script and function calls
Scilab scripts and functions are ASCII files
To re-use a previous command type the up arrow

Help
help opens a new window where browse for commands and searchkeywords
help name fun opens the help window directly at the pagecorresponding to the function name fun
An on-line help is available http://www.scilab.org/product/man/
A comparison between Matlab/Scilab function inhttp://www.scilab.org/product/dic-mat-sci/M2SCI doc.htm

Variables
A variable can be defined simply with the syntax
-->name = instruction;
The ; symbol prevents to print on screen the results
Standard rules common to languages as C or Pascal apply for Scilabvariables
Names are case sensitive: a 6=ATo see the variable value just type its name on the prompt or use thetool browsevar()

Workspace
Variables and functions stay in the workspace
commands of general use are
who
who_user
clear
load
save
diary
browsevar()

Variable types
A specific set of operators is available for the corresponding type
Common types are
constant , polynomial , function , handle ,
string , boolean , list , rational ,
state -space , sparse , boolean sparse
The type of a variable can be obtained
typeof(variable_name)

Write protected variables
Certain variables are predefined and write-protected%i i =
1 immaginary unit
%pi = 3.1415927 . . . pi grek%e e = 2.718281 . . . number of Nepero%eps = 2.2 1016 precision (machine dependent)%inf infinity%nan NotANumber%s s polynomial variable%z z polynomial variable%t true boolean variable%f false boolean variable

Matrices
To insert a matrix the syntaxes are
-->A = [1, 2, 3; 4, 5, 6; 7, 8, 9];
-->A = [1, 2, 3
-->4 5 6
-->7,8,9]
A =
1. 2. 3.
4. 5. 6.
7. 8. 9.

Scalars and vectors
Scalars and vectors are matrices!
-->a=[1 3 5];
-->size(a)
ans =
1. 3.
-->b=3;size(b)
ans =
1. 1.

Incremental vectors
-->x=1:4
x =
1. 2. 3. 4.
-->x=1:2:10
x =
1. 3. 5. 7. 9.
Also available linspace(x0,xf,npti) and logspace(...)

Accessing matrix elements
A(i,j) access the element in row i and column j
A(2,4:6) select the columns from 4 to 6 of the second row
B=A(1:3,4:6) assign to B the selected submatrix
A(:,5) select the column 5
A([1 3],5) select a 1x2 vector of two elements: A(1,5) and A(3,5)

Matrix operations
A wide number of operations are available, in addition to the basicoperations such as sum, product, transpose, matrix esponential,inverse, rank, kernel, etc.
A library of operations are available under the Linear Algebra sectionof the help
Some operations are also defined to be performed on the singleelements of the matrix

Polynomial operations
Defining a variable as polynomial allows to access several specificoperations
-->my_pol = 3*%s^2 + 2*%s
my_pol =
2
2s + 3s
-->roots(my_pol)
ans =
0
- 0.6666667

Polynomial operations
Define a polynomial from the coefficient: poly
Define a polynomial from its expression (previous example)
Define a polynomial by operations on elementary polynomials
Extract the coefficients of a polynomial: coeff
Evaluate the polynomial in one single point: horner
Symbolic substitution of the polynomial variable with another

Rational operations
Rational functions are the division between two polynomials
Several commands defined to their use similar to the polynomial type

Script
It is a collection of commands saved in a single ASCII file whoseextension is conventionally .sce
It is executed typing
-->exec(file_name.sce);

Functions
A function is a piece of code returning an output given several inputswhose syntax is
function [y1 ,...,ym] = fun(x1 ,...,xn)
commands
endfunction
Several functions can be saved in a single ASCII file whose extensionis conventionally .sci

Functions
User-defined functions are not available until not explicitely called bygetf(name file.sci)
Loading, saving or clearing the variables causes Scilab to do the sameto the functions!
Functions see all the workspace
Inputs are passed by reference if the function does not change theirvalue otherwise by copy

Programming
Common programming constructions
for, end
while, end
if, then, else, end
select, case, else, end
Logical operators: & | & and| or not

Load/Save data
Data in the workspace can be saved in a binary file:save(name file)
Data previously saved can be loaded in the workspace:load(name file)
C and Fortran-like commands are available to save formatted data inASCII files
Data saved with older version of Matlab can also be loaded

Graphics
Graphics commands are executed on windows different from the mainone (the Scilex window)
To create a new graphic window
xset(window ,num)
scf(num)
General windows-related commands are
clf(num), xclear(num),
xselect(), xdel(num)

Plot2d
The command plot2d draws bidimentional curves
It uses the current graphic window superimposing the curves
It creates a new graphic window if none is open
Several drawing possibilities depending on the syntax
plot2d ([x],y,)

Plot2d
plot2d(x,y) where x and y are vectors of the same size draws a curvewith x data in the horizontal and y data in vertical axes
plot2d(y) where y is a vector assumes x=1:n
plot2d(x,y) where x is a vector and y is a matrix assumes the samehorizontal data for the columns of y
plot2d(x,y) where x and y are matrices draws each column of yversus the corresponding column of x

Plot2d
Let us draw a sinusoidal signal with = 5 and phase = /4 for twoperiods
-->w=5;f=%pi/4;tf=(4*%pi -%pi/4)/w;
-->t=linspace(0,tf ,100);plot2d(t,sin(w*t+f))
Refer to the syntax to change colors, add symbols, add labels, title,etc.

Understanding a graphic window
The graphic window is an object containing several childs: figure,axis, curves
In the previous example the relationship is given by
Figure (1)
- Axes(1)
- Compund(1)
- Polyline(1)

Modyfing the graphic properties
A GUI opens with the command xset() that allows to change thegraphic context
From the graphic window it is possible to browse the properties of theobjects under the menu [edit]
From a script/function it is possible to have an handle to an objectand modyfing its parameters
h=gcf()
h=gca()
h=gce()

More axes on the same figure
The subplot(ijk) command divides the figure in a matrix of i rowsand j columns and select the k element
subplot(211); plot2d(ya)
subplot(212); plot2d(yb)

Exporting your figure
Several commands exist to export your figure such as
xs2eps , xs2fig , xs2gif ,
xs2ppm , xs2ps
and, only for Windows,
xs2bmp

Introduction to Scilab 5.3 and Xcos - · PDF fileRunning Scilab From Linux or Windows just...

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