Introduction to Scientific Computing Tool Scilab

Transcription

1 Introduction to Scientific Computing Tool Scilab Chao Chieh Lan and Jian Hao Liou Department of Mechanical Engineering National Cheng Kung University 2009/09/22 1

2 Computing Tools for Mechanism Analyses Low level Medium level High level C++ Fortran Mathematica Matlab Working Model ADAMS Low level: l General purpose Fast computation Matrix manipulation is cumbersome No direct graphics support Difficult to debug Medium level: Matrix manipulation is easy Direct graphics support Less general Slower computation High level: Easy to debug Graphical user interface You don t know if the software cheat you! 2

3 Scilab A Free Alternative to Matlab Scilab is a scientific software package for numerical computations. It was initially developed by INRIA and ENPC in France. Scilab is an open source software. Since 1994 it has been distributed freely alongwiththe the source code via the Internet. Now, the latest edition is Scilab syntax is largely based on the MATLAB language. Other free alternatives to Matlab include Octave and RlabPlus. 3

4 Scilab Layout Command window: *.sce is a script file that you can store you program. *.sci is a function file that you can store you frequently used subroutines. Scipad: You can edit *.sce file and *.sci files here 4

5 Basic Operations The simplest way to execute scilab code is to type it in at the prompt, >>, in the graphical command window. Scilab doesn t need to declare a variable before using it. No pointers are required either. Scilab is a case sensitive software. For example: A=[1 2;3 4]; but a is not equal to A Use ; after the command to suppress output to screen. π = %pi, imaginary number =%i, %e = Lines after // are comments. Use to split a long line into two lines. atan(p/q): 2 quadrant inverse tangent; atan(p,q): 4 quadrant inverse tangent Cross product:no such command for Scilab. You have to write it by yourself. Scilab is 1 indexing, different from C++ which is 0 indexing. 5

6 Matrix Manipulations (1) The row elements of matrix are separated by space or comma (,) ; the column elements of matrix are separated by semicolon (;), for example: A=[1 2 3;4 5 6] A=[ ] (2) The multiplication and product of matrices: A=[ ] B=[ ] The multiplication li li i of A and B is A*B or A *B the product of A Bis A.* B (3) Set A is a matrix, A is the transposition matrix of A. A=[ A[ ] A =[ ] (4) Denotes the solution to the matrix equation AX = B. ifa1*x1+a2*x2=b1 a1*x1+a2*x2=b1, a3*x1+a4*x2=b2 Set A=[ ], B=[ ], x=[ ] X=A\B (5) Colon is a very useful tool in Scilab. 6

7 Programming: Loop and Conditional Control (1) for :for index = start : increment : end statements end (2) while : (3) if : (4) break :it can while expression if logical expression then interrupt loops. statements statements else then end statements end 7

8 Programming Tips and Useful Commands Put the command clear and close in the very beginning of a *.sce sce script file to delete previous results. Put a command pause in between the lines to serve as a break point. Use return to continue executing. Use command who_user to list user s defined variables. browsevar(): an embedded function which you can browse and edit existing variables. abes fsolve: find a zero of a system of n nonlinear functions. Its calling sequence is [x]=fsolve(x0 [] e(0, fun, tol), x is the eoptimizer solution, o x0 is the initial ta value aue which you starting guess at the solution, fun is the function that you want to solve, and tol is the precision tolerance. 8

9 Programming of Function (1) Edit the function on SciPad (2) cross is the function name. You can name it by yourself. (3) f is the output of the function. u1, u2, u3, v1,v2 and v3 are the input parameters of the function. (4) Save the file as cross.sci (5) Load the function:exec( file path ) and the you can execute it (6) The variables defined inside the function are local. They do not affect the variables outside the function. 9

10 Graphics:Plot (1) xinit: Open a new graphic. If you don t do this data will be plotted in the same graphic. (2) plot(x,y): Use this command to plot the curve about the relationship of x and y, where x and y are both vectors. (3) locate(i,1): (i1) Find out the location of the points(p1,p2.pi) i) (a) the points which you choose. (b) the coordinates of the points. 10

11 Graphics:Line Properties (1) Use the commend ged() to change the properties of figure. (2) Choose the item that you want to change its properties. (3) Change type and width of the curve. (4) Change the color of the curve. 11

12 Graphics:Axes Properties (1) Key in the label of axes. (2) Choose the item to adjust the properties of axes. (3) Change the font size of label. (4) The font size of the axes. 12

13 Graphics:Export and Print (1) Choose file Export (2) Choose the Export type item, and decide the file type that you want to save. File Print Postscript 13

14 Animation of mechanisms Slider crank mechanism demo (ex 4.3, p140 of Cleghorn) 14

15 Animation of cams (ex 8.7, p.397 of Waldron) Oscillating Roller Follower 15

16 Scilab Browse Help and Web Resources Scilab hompage The instruction of Scilab (1) The instruction of Scilab (2) / l / l/ b h 16