Scilab Programming. The open source platform for numerical computation. Satish Annigeri Ph.D.

Transcription

1 Scilab Programming The open source platform for numerical computation Satish Annigeri Ph.D. Professor, Civil Engineering Department B.V.B. College of Engineering & Technology Hubli Sep, 2010 Satish Annigeri Ph.D. (BVBCET, Hubli) Scilab Programming 27 Sep, / 38

2 About Scilab Introduction Scilab is an open source numerical computation platform Multiplatform - Windows, Linux, Mac OS X, Solaris, Unixes An interactive numerical tool Matrices are a built-in data type in Scilab All operations on matrices are built-in Has a scripting programming language to write functions and develop libraries Has 2D and 3D graph plotting capabilities Has a large number of libraries contributed by the community Image Processing, Optimization, Genetic Algorithms, Neural Networks LabView Gateway - connects NI LabView with Scilab and access Scilab s power within LabView Xcos - hybrid dynamic systems modeller and simulator Interfaces with code written in Fortran, C, C++ Embeddable - Scilab/Xcos C code generator for FLEX board Satish Annigeri Ph.D. (BVBCET, Hubli) Scilab Programming 27 Sep, / 38

3 Introduction Current Status of Scilab Current version is beta 3 Scicos is now called Xcos New improved code editor Dockable application windows - Editor, Graphics window New architecture for modular plug-ins - ATOMS Satish Annigeri Ph.D. (BVBCET, Hubli) Scilab Programming 27 Sep, / 38

4 Scilab Applications Introduction Civil Engineering Matrix structural analysis, Finite element analysis Xcos - Mechanical vibration, Hydraulic circuit analysis Electrical Sciences Xcos - Circuit simulation Filter design Image processing Control systems Hardware interfacing, Sensors, Embedded systems Mechanical Sciences Robotics Finite element analysis Computer Science Graph theory Image processing ANN, GA, Fuzzy logic Satish Annigeri Ph.D. (BVBCET, Hubli) Scilab Programming 27 Sep, / 38

5 Agenda Introduction Scilab Programming Language Data types, Operators, Expressions, Statements Script files Functions, Input and output arguments, Variable number of arguments File Operations Opening and closing files Reading from files Writing to files Reading Microsoft Excel files Writing CSV text files Satish Annigeri Ph.D. (BVBCET, Hubli) Scilab Programming 27 Sep, / 38

6 Scilab Resources Introduction Scilab Website Scilab website - Xcos website - Scilab documentation - Extending Scilab - zone/extensions Tools for Scilab development - zone/tools Scilab Tutorials Tutorial on Scilab website - My Lulu webpage has two tutorials Introduction to Scilab - Matrix Structural Analysis of Plane Frames - Satish Annigeri Ph.D. (BVBCET, Hubli) Scilab Programming 27 Sep, / 38

7 Introduction Preliminaries Scilab can be used in interactive mode like a calculator Scilab can be used in batch mode to execute a set of commands written in a file, called a script file. Scilab can be used to write functions like any other programming language Global local variables Argument passing mechanism Scilab is weakly typed - No stringent restrictions on type declaration, type conversion Scilab is case sensitive Output of a command is immediately echoed on the console Multiple commands on the same line can be separated by a comma (,) or a semicolon (;) A semicolon (;) at the end of a statement suppresses echoing of output from the statement Single line comments begin with // and last up to the end of the line Satish Annigeri Ph.D. (BVBCET, Hubli) Scilab Programming 27 Sep, / 38

8 Introduction Scilab Environment Scilab command prompt is: --> Access to on-line help Type -->help Press F1 From the menu choose? = Scilab Help On-line help offers two choices Table of contents Search for specific patterns Direct access to help on Scilab functions: -->help pattern Scilab constants π: %pi ɛ: %eps NaN: %nan e: %e i = 1: %i inf: %inf Satish Annigeri Ph.D. (BVBCET, Hubli) Scilab Programming 27 Sep, / 38

9 Introduction Scilab Variables Variable names follow the same convention as in C Names can contain alphanumeric characters Names must begin with an alphabet An 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 any other Scilab data type Satish Annigeri Ph.D. (BVBCET, Hubli) Scilab Programming 27 Sep, / 38

10 Scilab Workspace Introduction 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 Constant String Boolean Function Library Polynomial Rational Cell (ce) List Struct (st) Satish Annigeri Ph.D. (BVBCET, Hubli) Scilab Programming 27 Sep, / 38

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

12 Introduction Matrix Operations in Scilab Defining matrices Matrices are enclosed between square brackets Elements are defined row by row. All rows must contain the same number of columns Elements in a row can be separated by a comma or a space Rows are separated by a semi colon or by a carriage return Semi 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 = a b Left division c = a b Same as c = a 1 b or c = b a Transpose b = a Power b = a 2 or b = a**2 Satish Annigeri Ph.D. (BVBCET, Hubli) Scilab Programming 27 Sep, / 38

13 Introduction Automating Scilab Initially you may be contented using Scilab as a powerful interactive calculator matrix computations graphics rich 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 Language We will learn how to write Scilab functions We will learn how to write Scilab script files Satish Annigeri Ph.D. (BVBCET, Hubli) Scilab Programming 27 Sep, / 38

14 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 Scilab programming language. Your knowledge of using Scilab interactively becomes the starting point for programming Offers features expected from a traditional procedural languages: Data types: Built-in and User-defined Control structures: if then else if, for, do, select Functions: input arguments, output arguments, input and output arguments Does not currently support object oriented programming Satish Annigeri Ph.D. (BVBCET, Hubli) Scilab Programming 27 Sep, / 38

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

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

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

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

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

20 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 Odd numbers between 1 and 5 -->for i = 1:2:5, disp(i), end Satish Annigeri Ph.D. (BVBCET, Hubli) Scilab Programming 27 Sep, / 38

21 Control Structures for Loop Even numbers between 1 and 5 -->for i = 2:2:6, disp(i), end With fractional increment -->for dx = 0:%pi/16:%pi, disp(dx), end In reverse gear, if you so wish -->for dx = 10:-2:5, disp(dx), end Satish Annigeri Ph.D. (BVBCET, Hubli) Scilab Programming 27 Sep, / 38

22 for Loop Control Structures Every for loop must close with a corresponding end, no matter what the 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 as values the values of each column of the matrix or row vector If expression is a list variable, then variable takes as values the successive entries of the list for loop can be interrupted with the break statement, forcing the end 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 Satish Annigeri Ph.D. (BVBCET, Hubli) Scilab Programming 27 Sep, / 38

23 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 alternative a = 2 -->if a < 0 then --> disp( Negative ) -->else -->disp( Non-negative ) -->end Non-negative Satish Annigeri Ph.D. (BVBCET, Hubli) Scilab Programming 27 Sep, / 38

24 Control Structures if then elseif else Multiple test with an alternative a = -2 -->if a < 0 then --> disp( Negative ) Negative -->elseif a == 0 then -->disp( Zero ) else -->disp( Positive ) -->end Notice that the word Negative is displayed even before you complete the if block. This is because of short-circuiting of boolean expression evaluation. If this alternative is true, then others need not be evaluated. Try this loop with different values of a Satish Annigeri Ph.D. (BVBCET, Hubli) Scilab Programming 27 Sep, / 38

25 select is useful when the number of tests in a if block is large. But can handle only equal to comparisons and not inequalities. It is similar 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! ) -->end Satish Annigeri Ph.D. (BVBCET, Hubli) Scilab Programming 27 Sep, / 38 select Control Structures

26 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 workspace Output 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 in C programming language) Satish Annigeri Ph.D. (BVBCET, Hubli) Scilab Programming 27 Sep, / 38

27 Scilab Functions Scilab Functions Functions help modularize code They define a well defined interface to the function and serve as a means of communication between the designer of the function and the consumer of the function Function interface consists of Name of the function - usually indicates the purpose of the function. Purpose is further explained in the documentation Input arguments - variables sent into the function from the calling module. Appear on the RHS of assignment statements. Output arguments - variables whose values are calculated inside the function and sent out to the calling module. Appear on the LHS of assignment statements. Calling a function invokes the function. Variables in the function call are called input and output parameters. Number and type of arguments (as in the function definition) and parameters (as in the function call) must match. Satish Annigeri Ph.D. (BVBCET, Hubli) Scilab Programming 27 Sep, / 38

28 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 arguments Function name must be chosen to reflect its purpose Function name can consist of alphanumeric characters First character must be an alphabet Underscore 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 lasts until the end of line Satish Annigeri Ph.D. (BVBCET, Hubli) Scilab Programming 27 Sep, / 38

29 Scilab Functions Function to Calculate Length of a Line Consider two points on a plane P 1 (x 1, y 1 ) and P 2 (x 2, y 2 ) The length between the two points is L = (x 2 x 1 ) 2 + (y 2 y 1 ) 2 Let us write a simple function to obtain the length and make a few improvements to increase its usefulness. Scilab has a built-in code editor named SciPad Syntax color highlighting Edit and save code All 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 Satish Annigeri Ph.D. (BVBCET, Hubli) Scilab Programming 27 Sep, / 38

30 Scilab Functions Use the Scilab Function Save the function into a file in a known folder. Note down the folder 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. Satish Annigeri Ph.D. (BVBCET, Hubli) Scilab Programming 27 Sep, / 38

31 Test the Function Scilab Functions 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 P 1 (x 1, y 1, z 1 ) and P 2 (x 2, y 2, z 2 ). L = (x 2 x 1 ) 2 + (y 2 y 1 ) 2 + (z 2 z 1 ) 2 Improve the function Instead of giving coordinates (x 1, y 1, z 1 ) and (x 2, y 2, z 2 ) as input, give vectors with coordinates p1 and p2 as input. Point p1 can be (x 1, y 1 ) or (x 1, y 1, z 1 ) depending on whether you want it to be a point in a plane or in space. Make the function work for points in a plane as well as in space Satish Annigeri Ph.D. (BVBCET, Hubli) Scilab Programming 27 Sep, / 38

32 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 two coordinates 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. Satish Annigeri Ph.D. (BVBCET, Hubli) Scilab Programming 27 Sep, / 38

33 Scilab Functions Function with Two Output Parameters function [L, dx] = Len(p1, p2) dx = p2 - p1; L = sqrt(sum(dx. 2)) endfunction You can use this function in different ways. If you only want the length 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 = L = 5. Satish Annigeri Ph.D. (BVBCET, Hubli) Scilab Programming 27 Sep, / 38

34 Scilab Functions Some Tips and Tricks Choose names of functions with care Not too cryptic Not too long Meaningful, 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 before using them If necessary, check the number of input and output parameters at run time. There is no guarantee that the number of parameters are the same as the number of arguments It is allowed to have a variable both as an input and as an output argument. Typically, such a variable brings in a value in it, gets modified within the function and the changed value is sent back Satish Annigeri Ph.D. (BVBCET, Hubli) Scilab Programming 27 Sep, / 38

35 Scilab Functions Further Improved Scilab Function function [L dx] = Len(p1, p2) [lhs, rhs] = argn() if rhs < 2 then disp( Too few arguments. L = 0; dx = []; return end dx = p2 - p1 L = sqrt(sum(dx. 2)) endfunction Returning from function ) Satish Annigeri Ph.D. (BVBCET, Hubli) Scilab Programming 27 Sep, / 38

36 Scilab Functions Short Inline Functions Short functions can be defined inline deff( [L]=Len(p1, p2), L=sqrt(sum((p2 - p1) 2)) ) Function deff(string1, string2) takes two strings as input parameters First string is the interface to the function, consisting of output arguments, function name and input arguments Second string consists of statements making up the body of the function If body contains more than one statement, they must be defined as elements of a vector deff( [L]=Len(p1, p2), [ dx=p2 - p1 ; L=sqrt(sum((dx) 2)) ]) Satish Annigeri Ph.D. (BVBCET, Hubli) Scilab Programming 27 Sep, / 38

37 Scilab Functions Some Closing Thoughts on Functions Functions can be called in other functions, and you can build a hierarchy of functions Simple functions are independent of other user defined functions and do 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 processing genetic algorithms structural optimization These become toolboxes when packaged in a specified way and bundled along with documentation Satish Annigeri Ph.D. (BVBCET, Hubli) Scilab Programming 27 Sep, / 38

38 Scilab Functions Thank You Satish Annigeri Ph.D. (BVBCET, Hubli) Scilab Programming 27 Sep, / 38