scilab programming - the open source platform for...

Scilab ProgrammingThe open source platform for numerical computation

Satish Annigeri Ph.D.

Professor, Civil Engineering DepartmentB.V.B. College of Engineering & Technology

Hubli 580 [email protected]

27 Sep, 2010

Satish Annigeri Ph.D. (BVBCET, Hubli) Scilab Programming 27 Sep, 2010 1 / 38

Introduction

About Scilab

Scilab is an open source numerical computation platform

Multiplatform - Windows, Linux, Mac OS X, Solaris, Unixes

An interactive numerical toolMatrices are a built-in data type in ScilabAll operations on matrices are built-in

Has a scripting programming language to write functions and developlibraries

Has 2D and 3D graph plotting capabilities

Has a large number of libraries contributed by the communityImage Processing, Optimization, Genetic Algorithms, Neural NetworksLabView Gateway - connects NI LabView with Scilab and accessScilab’s power within LabViewXcos - hybrid dynamic systems modeller and simulator

Interfaces with code written in Fortran, C, C++

Embeddable - Scilab/Xcos C code generator for FLEX board


Introduction

Current Status of Scilab

Current version is 5.3.0 beta 3

Scicos is now called Xcos

New improved code editor

Dockable application windows - Editor, Graphics window

New architecture for modular plug-ins - ATOMS


Introduction

Scilab Applications

Civil Engineering

Matrix structural analysis, Finite element analysisXcos - Mechanical vibration, Hydraulic circuit analysis

Electrical Sciences

Xcos - Circuit simulationFilter designImage processingControl systemsHardware interfacing, Sensors, Embedded systems

Mechanical Sciences

RoboticsFinite element analysis

Computer Science

Graph theoryImage processingANN, GA, Fuzzy logic


Introduction

Agenda

Scilab Programming Language

Data types, Operators, Expressions, StatementsScript filesFunctions, Input and output arguments, Variable number of arguments

File Operations

Opening and closing filesReading from filesWriting to filesReading Microsoft Excel filesWriting CSV text files


Introduction

Scilab Resources

Scilab Website

Scilab website - http://www.scilab.orgXcos website - http://www.scilab.org/products/xcosScilab documentation - http://www.scilab.org/support/documentationExtending Scilab -http://www.scilab.org/communities/developer zone/extensionsTools for Scilab development -http://www.scilab.org/communities/developer zone/tools

Scilab Tutorials

Tutorial on Scilab website -http://www.scilab.org/support/documentation/tutorialsMy Lulu webpage has two tutorials

Introduction to Scilab - http://bit.ly/bB5GHLMatrix Structural Analysis of Plane Frames - http://bit.ly/cXjoG4


http://www.scilab.org

http://www.scilab.org/products/xcos

http://www.scilab.org/support/documentation

http://www.scilab.org/communities/developer_zone/extensions

http://www.scilab.org/communities/developer_zone/tools

http://www.scilab.org/support/documentation/tutorials

http://bit.ly/bB5GHL

http://bit.ly/cXjoG4

Introduction

Preliminaries

Scilab can be used in interactive mode like a calculator

Scilab can be used in batch mode to execute a set of commandswritten in a file, called a script file.

Scilab can be used to write functions like any other programminglanguage

Global local variablesArgument passing mechanismScilab is weakly typed - No stringent restrictions on type declaration,type conversion

Scilab is case sensitiveOutput of a command is immediately echoed on the consoleMultiple commands on the same line can be separated by a comma (,)or a semicolon (;)A semicolon (;) at the end of a statement suppresses echoing ofoutput from the statementSingle line comments begin with // and last up to the end of the line


Introduction

Scilab Environment

Scilab command prompt is: -->

Access to on-line helpType -->help

Press F1

From the menu choose ? =¿ Scilab Help

On-line help offers two choicesTable of contentsSearch for specific patterns

Direct access to help on Scilab functions: -->help pattern

Scilab constantsπ: %pi

ε: %eps

NaN: %nane: %e

i =√−1: %i

inf: %inf


Introduction

Scilab Variables

Variable names follow the same convention as in C

Names can contain alphanumeric charactersNames must begin with an alphabetAn underscore character is treated as an alphabet

Variables can be assigned values

Name of a variable in an expression evaluates to its value

Value may be a real number, imaginary number, matrix, string or anyother Scilab data type


Introduction

Scilab Workspace

Examine the Scilab workspace

List names of contents of workspace: -->who

Detailed list of contents of workspace: -->whos

List names of constants: -->whos -type constant

List names of contents beginning with ”a”: -->whos -name a

Objects can be of the following data types

ConstantStringBooleanFunctionLibraryPolynomialRationalCell (ce)ListStruct (st)


Introduction

Scilab Workspace

Save entire contents of the workspace to a disk file

Save selected variables from the workspace to a disk file

Clear entire contents of the workspace

Clear selected variables from the workspace

Load data from a previously save workspace


Introduction

Matrix Operations in Scilab

Defining matrices

Matrices are enclosed between square bracketsElements are defined row by row. All rows must contain the samenumber of columnsElements in a row can be separated by a comma or a spaceRows are separated by a semi colon or by a carriage returnSemi colon at the end of the last row is optional

Simple matrix operations on two matrices a and b

Addition c = a + b

Subtraction c = a - b

Multiplication c = a * b

Right division c = a / b Same as c = a ∗ b−1 or c = ab

Left division c = a b Same as c = a−1 ∗ b or c = ba

Transpose b = a’

Power b = a∧2 or b = a**2


Introduction

Automating Scilab

Initially you may be contented using Scilab as a powerful interactivecalculator

matrix computationsgraphicsrich set of built-in functions

You will soon begin to yearn for more

Can I store repeated commands and execute them all at once?

Can I modularize repeated tasks and call them when I need?

Answer to both the questions is: Yes

We will take this up in three steps:

We will take a look at the Scilab Programming LanguageWe will learn how to write Scilab functionsWe will learn how to write Scilab script files


Scilab Data Types

Scilab Programming Language

Scilab has a programming language of its own

Every command that can be typed at the Scilab command prompt(without generating an error of course!) is a valid statement in Scilabprogramming language.

Your knowledge of using Scilab interactively becomes the startingpoint for programming

Offers features expected from a traditional procedural languages:

Data types: Built-in and User-definedControl structures: if then else if, for, do, selectFunctions: input arguments, output arguments, input and outputarguments

Does not currently support object oriented programming


Scilab Data Types

Scilab Data Types

Let us try our hand with a few Scilab data types

Constant-->a = rand(3,3)*10;

-->typeof(a)

constant

Boolean-->b = a < 5;

-->typeof(b)

boolean

Function -->whos

-->typeof(whos)

function

String -->s = ’Satish’;

-->typeof(s)

string


Scilab Data Types

Scilab Data Types...

Polynomial-->p1 = poly([2 3 5], ’x’];

# polynomial in ’x’ with three roots 2 3 and 5

-->typeof(p1)

polynomial

Rational-->p2 = poly([1 4], ’x’);

-->p3 = p1 / p2;

-->typeof(p3)

rational

Structure-->x.name = ’Satish’;

-->x.salary = 20e3;

-->typeof(x)

st


Scilab Data Types

Scilab Data Types...

Other data types available in Scilab are:

Handle

List

State-Space

Sparse - for sparse matrices

Boolan Sparse - for boolean sparse matrices

Hypermat - N dimension array with N ¿= 3

Cell - Cell array

fptr - Scilab intrinsic (C or Fortran code)

Pointer

Size Implicit


Operators

Operators

[ ] Matrix definition( ) Extraction, eg. m = a(k)’ Transpose− Subtraction\ Left division∧ Exponent.\ Elementwise left division.∧ Elementwise exponent; Statement separator( ) Insertion, eg. a(k) = m+ Addition* Multiplication/ Right division.* Elementwise multiplication./ Elementwise right division


Control Structures

Control Structures

Loop Constructs

for - Repeat a block of statements based on an index variable

while - Conditional repetition of a block of statements

Select Constructs

if then, if then else, if then elseif else

select - similar to switch in C


Control Structures

for Loop

In its simplest form, let us use a for loop to print a sequence of numbers

Numbers 1 to 5-->for i = 1:5

-->disp(i)

-->end

1.

2.

3.

4.

5.

Odd numbers between 1 and 5-->for i = 1:2:5, disp(i), end

1.

3.


Control Structures

for Loop

Even numbers between 1 and 5-->for i = 2:2:6, disp(i), end

2.

4.

With fractional increment-->for dx = 0:%pi/16:%pi, disp(dx), end

0.

0.1963495

...

3.1415927

In reverse gear, if you so wish-->for dx = 10:-2:5, disp(dx), end

10.

8.

6.


Control Structures

for Loop

Every for loop must close with a corresponding end, no matter whatthe depth of nesting is

Another accepted form of the for loop is with the keyword do

for variable = expression do

statement

end

If expression is a matrix or a row vector, then variable takes asvalues the values of each column of the matrix or row vector

If expression is a list variable, then variable takes as values thesuccessive entries of the list

for loop can be interrupted with the break statement, forcing theend of the innermost for loop

One cycle of for loop can be skipped with the continue keyword

Other means of interfering with the for loop are:pause, return and abort


Control Structures

if then, if then else

General format of if in different combinations is

Only one test-->a = -2;

-->if a < 0 then

--> disp(’Negative’)

-->end

Negative

One test with an alternativea = 2

-->if a < 0 then


-->else

-->disp(’Non-negative’)

-->end

Non-negative


Control Structures

if then elseif else

Multiple test with an alternativea = -2

-->if a < 0 then


Negative

-->elseif a == 0 then

-->disp(’Zero’)

else

-->disp(’Positive’)

-->end

Notice that the word Negative is displayed even before you completethe if block. This is because of short-circuiting of boolean expressionevaluation. If this alternative is true, then others need not beevaluated.

Try this loop with different values of a


Control Structures

select

select is useful when the number of tests in a if block is large. Butcan handle only ”equal to” comparisons and not inequalities. It issimilar to the switch block in C.-->ch = input(’Enter an integer: ’);

3

-->select ch

-->case 1 then

-->disp(’One’)

-->case 2 then

-->disp(’Two’)

-->case 3 then

-->disp(’Three’)

Three

-->else

-->disp(’Dah!’)

-->endSatish Annigeri Ph.D. (BVBCET, Hubli) Scilab Programming 27 Sep, 2010 25 / 38

Control Structures

Script Files

Script files are text files containing Scilab statements

There is no separate workspace for the script file

The statements take their input from the Scilab workspaceOutput generated by the statements are stored in the Scilab workspace

Useful for testing and debugging statements

Useful to write the main program (similar to the main() function inC programming language)


Scilab Functions

Scilab Functions

Functions help modularize code

They define a well defined interface to the function and serve as ameans of communication between the designer of the function andthe consumer of the functionFunction interface consists of

Name of the function - usually indicates the purpose of the function.Purpose is further explained in the documentationInput arguments - variables sent into the function from the callingmodule. Appear on the RHS of assignment statements.Output arguments - variables whose values are calculated inside thefunction and sent out to the calling module. Appear on the LHS ofassignment statements.

Calling a function invokes the function. Variables in the function callare called input and output parameters.

Number and type of arguments (as in the function definition) andparameters (as in the function call) must match.


Scilab Functions

Scilab Function Skeleton

function [out1, out2, ...] = function-name(in1, in2, ...)

statement-1;

statement-2;

...

statement-n;

endfunction

Function definition begins with the keyword function

A function can have one or more output argumentsFunction name must be chosen to reflect its purpose

Function name can consist of alphanumeric charactersFirst character must be an alphabetUnderscore is treated as an alphabet

A function can have zero or more input arguments

Function definition ends with the keyword endfunction

A comment is begun by a pair of forward slashes (//) and lastsuntil the end of line


Scilab Functions

Function to Calculate Length of a Line

Consider two points on a plane P1(x1, y1) and P2(x2, y2)

The length between the two points is L =√

(x2 − x1)2 + (y2 − y1)2

Let us write a simple function to obtain the length and make a fewimprovements to increase its usefulness.

Scilab has a built-in code editor named SciPad

Syntax color highlightingEdit and save codeAll features of a code editor - search, search and replace, save as etc.Compile source code and load into Scilab workspace

function [L] = Len(x1, y1, x2, y2)

// Returns length of line between (x1,y1) and (x2,y2)

dx = x2 - x1;

dy = y2 - y1;

L = sqrt(dx∧2 + dy∧2);endfunction


Scilab Functions

Use the Scilab Function

Save the function into a file in a known folder. Note down thefolder location and filename for later use.

In SciPad, click on Execute ⇒ Load into Scilab

Switch to Scilab and confirm the function is loaded into the workspace-->whos -type function

Name Type Size Bytes

....

Len function 664

Call the function with known input and test the output-->Len(0, 0, 4, 3)

ans =

5.


Scilab Functions

Test the Function

Give input in different ways and test-->x1=0; y1=0; x2=4; y2=3;

-->Len(x1, y1, x2, y2)

ans =

5.

Identify its shortcomings

Does not adapt itself to points in 3D space P1(x1, y1, z1) andP2(x2, y2, z2). L =

√(x2 − x1)2 + (y2 − y1)2 + (z2 − z1)2

Improve the function

Instead of giving coordinates (x1, y1, z1) and (x2, y2, z2) as input, givevectors with coordinates p1 and p2 as input. Point p1 can be (x1, y1)or (x1, y1, z1) depending on whether you want it to be a point in aplane or in space.Make the function work for points in a plane as well as in space


Scilab Functions

Test Improved Function

function [L] = Len(p1, p2)

dx = p2 - p1; // works for points in 2D as well as 3D

L = sqrt(sum(dx.∧2))endfunction

This time around, input consists of two points, each point having twocoordinates arrnged as two elements in a vector-->Len([0, 0], [4, 3])

ans =

5.

Try a point in space-->Len([0, 0, 0], [4, 3, 0])

ans =

5.


Scilab Functions

Function with Two Output Parameters

function [L, dx] = Len(p1, p2)

dx = p2 - p1;


You can use this function in different ways. If you only want thelength and not the projections along the axes-->L = Len([0 0 0], [4 3 0])

L =

5.

When you want to use both output parameters-->[L dxdydz] = Len([0 0 0], [4 3 0])

dxdydz =

3. 4. 5.

L =

5.


Scilab Functions

Some Tips and Tricks

Choose names of functions with care

Not too crypticNot too longMeaningful, reflecting the function’s purpose

Choose the input and output arguments after due process of thought

If some input arguments must be of a specified size, do check beforeusing them

If necessary, check the number of input and output parameters at runtime. There is no guarantee that the number of parameters are thesame as the number of arguments

It is allowed to have a variable both as an input and as an outputargument. Typically, such a variable brings in a value in it, getsmodified within the function and the changed value is sent back


Scilab Functions

Further Improved Scilab Function

function [L dx] = Len(p1, p2)

[lhs, rhs] = argn()

if rhs < 2 then

disp(’Too few arguments. Returning from function’)

L = 0; dx = [];

return

end

dx = p2 - p1



Scilab Functions

Short Inline Functions

Short functions can be defined inlinedeff(’[L]=Len(p1, p2)’, ’L=sqrt(sum((p2 - p1)∧2))’)

Function deff(string1, string2) takes two strings as inputparameters

First string is the interface to the function, consisting of outputarguments, function name and input arguments

Second string consists of statements making up the body of thefunction

If body contains more than one statement, they must be defined aselements of a vectordeff(’[L]=Len(p1, p2)’, [’dx=p2 - p1’;

’L=sqrt(sum((dx)∧2))’])


Scilab Functions

Some Closing Thoughts on Functions

Functions can be called in other functions, and you can build ahierarchy of functions

Simple functions are independent of other user defined functions anddo a simple task efficiently

Complex functions depend on other user defined functions

You can build a library of such functions for a well defined task

image processinggenetic algorithmsstructural optimization

These become toolboxes when packaged in a specified way andbundled along with documentation


Scilab Functions

Thank You


scilab programming - the open source platform for...

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