Introduction to Matlab

Transcription

1 Introduction to Matlab Weichung Wang 2003 NCTS-NSF Workshop on Differential Equations, Surface Theory, and Mathematical Visualization NCTS, Hsinchu, February 13, 2003 DE, ST, MV Workshop Matlab 1

2 Main Goals A brief Matlab introduction for beginners Warm-up for Prof. Karcher s courses DE, ST, MV Workshop Matlab 2

3 Start Matlab in Windows DE, ST, MV Workshop Matlab 4

4 Start Matlab in Unix shell In command line window, type > matlab > matlab -nojvm DE, ST, MV Workshop Matlab 5

5 What is Matlab? MATLAB == MATrix LABoratory Mathworks: Major software characteristics: matrix-based numeric computation high-level programming language graphics & visualization toolboxes provide application-specific functionality DE, ST, MV Workshop Matlab 6

6 What Is Matlab? (Cont.) Multi-platform support (PC / Macintosh / UNIX) Interfaces to other systems. Custom C, Fortran (MATLAB is callable) Extensive data I/O facility Matlab is case sensitive (mtxa ~= MTXA) DE, ST, MV Workshop Matlab 7

7 As a Calculator DE, ST, MV Workshop Matlab 8

8 Built-in Variables DE, ST, MV Workshop Matlab 9

9 Built-in Functions DE, ST, MV Workshop Matlab 10

10 Looking for Functions DE, ST, MV Workshop Matlab 11

11 On-line Help DE, ST, MV Workshop Matlab 12

12 Suppress Output With Semicolon DE, ST, MV Workshop Matlab 13

13 Multiple Statements Per Line DE, ST, MV Workshop Matlab 14

14 Vectors and Matrices DE, ST, MV Workshop Matlab 15

15 Matrix DE, ST, MV Workshop Matlab 16

16 Colon Notation DE, ST, MV Workshop Matlab 17

17 Colon Notation (Cont.) DE, ST, MV Workshop Matlab 18

18 Colon Notation (Cont.) DE, ST, MV Workshop Matlab 19

19 Complex Numbers DE, ST, MV Workshop Matlab 20

20 Complex Number (Cont.) DE, ST, MV Workshop Matlab 21

21 Complex Number (Cont.) DE, ST, MV Workshop Matlab 22

22 Manipulation of Matrices and Vectors DE, ST, MV Workshop Matlab 23

23 Vectorization DE, ST, MV Workshop Matlab 24

24 Vectorization (Cont.) DE, ST, MV Workshop Matlab 25

25 Array Operators DE, ST, MV Workshop Matlab 26

26 Array Operators (Cont.) DE, ST, MV Workshop Matlab 27

27 Array Operators (Cont.) DE, ST, MV Workshop Matlab 28

28 Plotting DE, ST, MV Workshop Matlab 29

29 Plotting (Cont.) DE, ST, MV Workshop Matlab 30

30 Case Study Examples by Prof. Hermann Karcher Set 1: FirstConventions.m (script) Change current directory to the directory containing the file FirstConventions.m DE, ST, MV Workshop Matlab 31

31 Script Give Orders by Command, Script, and Function Standard ASCII text files containing a sequence of normal MATLAB commands/statements. The command PlotSine causes the statements in the file named PlotSine.m to be parsed & executed in order. (Interpreter, not compiler.) % Comments start with "%" characte Variables in a script file are global. DE, ST, MV Workshop Matlab 32

32 Give Orders (cont.) Function Function files provide extensibility to MATLAB. Usually contains input and output. Variables in a function file are by default local. However, you can declare a variable to be global. DE, ST, MV Workshop Matlab 33

33 Flow Control Constructs Logic Control: if/ switch if I == J A(I,J) = 2; elseif abs(i-j) == 1 A(I,J) = -1; else A(I,J) = 0; end switch algorithm case 'ode23 str = '2nd/3rd order'; case {'ode15s', 'ode23s'} str = 'stiff system'; otherwise str = 'other algorithm'; end DE, ST, MV Workshop Matlab 34

34 Flow Control Constructs (cont.) Iterative Loops: for / while N = 10; for I = 1:N for J = 1:N A(I,J) = 1/(I+J-1); end end I = 1; N = 10; while I <= N end J = 1; while J <= N A(I,J) = 1/(I+J- 1); J = J+1; end I = I+1; DE, ST, MV Workshop Matlab 35

35 Structure of a Function M-file Keyword: function Function Name (same as file name.m) Output Argument(s) Input Argument(s) Online Help MATLAB Code function y = mean(x) % MEAN MEAN Average or or mean mean value. % For For vectors, MEAN(x) returns the the mean mean value. % For For matrices, MEAN(x) is is a row row vector % containing the the mean mean value of of each each column. [m,n] = size(x); if ifm == == 1 m = n; n; end end y = sum(x)/m;»output_value = mean(input_value) Command Line Syntax

36 Workspaces or Stacks in MATLAB MATLAB (or Base) Workspace: For command line and script file variables. Function Workspaces: Each function has its own workspace for local variables. Communicate to Function Workspace via inputs & outputs. (Promotes structured coding & prevents name conflicts.) Global Workspace: Global variables can be shared by multiple workspaces. (Must be initialized in all relevant workspaces.)

37 Inter-workspace Communication MATLAB Workspace Function inputs and outputs Function Workspace Initialize global variables in all relevant workspaces:»global variable_name Initialize global variables in the source workspace before referring to them from other workspaces. Global variables Global Workspace

38 Case Studies Examples by Prof. Hermann Karcher Set 2: ConCsqrt.m and Csqrt.m (both functions) DE, ST, MV Workshop Matlab 39

39 Some Suggestions Write comments % s=1 if scalar product(w,last) >=0 else s=-1 s=2*(real(w.*conj(last))>=0)-1; DE, ST, MV Workshop Matlab 40

40 Some Suggestions (Cont.) Give meaningful variable names and avoid single character variable names a=b*c; f=m*a; force = mass * acceleration; for ii=1:3 moment = ii^2; end; DE, ST, MV Workshop Matlab 41

41 Some Suggestions (Cont.) Indent codes Use Emacs ( Learn by doing! DE, ST, MV Workshop Matlab 42

42 If You Were Sleeping It s OK. Just remember two commands: >> lookfor keyword >> help command DE, ST, MV Workshop Matlab 43

43 Happy coding! :-)

44 Reference Matlab Slides by Gerald Recktenwald DE, ST, MV Workshop Matlab 45