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1 Introduction to M ATLAB Programming

2 Copyright  by The MathWorks, Inc. Programming - 2 Introduction to M ATLAB Section Outline Script Files Flow Control & Array Operations EVAL Command Functions Structural Syntax Variables & Workspaces Subfunctions and Private Functions Visual Debugging

3 Copyright  by The MathWorks, Inc. Programming - 3 Introduction to M ATLAB The MATLAB Path MATLAB Path: List of directories searched by MATLAB. (Includes \toolbox directories) Path Cache: List of \toolbox files & locations. Created at startup to increase speed. Only updated when PATH command is called. Working with the Path: Path Browser (PATHTOOL) PATH, ADDPATH, RMPATH

4 Copyright  by The MathWorks, Inc. Programming - 4 Introduction to M ATLAB MATLAB Editor/Debugger »edit

5 Copyright  by The MathWorks, Inc. Programming - 5 Introduction to M ATLAB Script M-files Standard ASCII text files Contain a series of MATLAB expressions (Typed as you would at the command line) Commands parsed & executed in order % Comments start with "%" character pause % Suspend execution - hit any key to continue. keyboard % Pause & return control to command line. % Type "return" to continue. break % Terminate execution of current loop/file. return % Exit current function % Return to invoking function/command line. % Comments start with "%" character pause % Suspend execution - hit any key to continue. keyboard % Pause & return control to command line. % Type "return" to continue. break % Terminate execution of current loop/file. return % Exit current function % Return to invoking function/command line.

6 Copyright  by The MathWorks, Inc. Programming - 6 Introduction to M ATLAB Flow Control Constructs Logic Control: IF / ELSEIF / ELSE SWITCH / CASE / OTHERWISE Iterative Loops: FOR WHILE

7 Copyright  by The MathWorks, Inc. Programming - 7 Introduction to M ATLAB The if, elseif and else statements if I == J A(I,J) = 2; elseif abs(I-J) == 1 A(I,J) = -1; else A(I,J) = 0; end if I == J A(I,J) = 2; elseif abs(I-J) == 1 A(I,J) = -1; else A(I,J) = 0; end »if_examp Works on Conditional statements Short-circuited in MATLAB - once a condition is true, the sequence terminates.

8 Copyright  by The MathWorks, Inc. Programming - 8 Introduction to M ATLAB Switch, Case, and Otherwise switch input_num case -1 input_str = 'minus one'; case 0 input_str = 'zero'; case 1 input_str = 'plus one'; case {-10,10} input_str = '+/- ten'; otherwise input_str = 'other value'; end switch input_num case -1 input_str = 'minus one'; case 0 input_str = 'zero'; case 1 input_str = 'plus one'; case {-10,10} input_str = '+/- ten'; otherwise input_str = 'other value'; end More efficient than elseif statements Only the first matching case is executed »switch_examp

9 Copyright  by The MathWorks, Inc. Programming - 9 Introduction to M ATLAB Similar to other programming languages Repeats loop a set number of times (based on index) Can be nested The for loop N=10; for I = 1:N for J = 1:N A(I,J) = 1/(I+J-1); end N=10; for I = 1:N for J = 1:N A(I,J) = 1/(I+J-1); end »for_examp

10 Copyright  by The MathWorks, Inc. Programming - 10 Introduction to M ATLAB The while loop I=1; N=10; while I<=N J=1; while J<=N A(I,J)=1/(I+J-1); J=J+1; end I=I+1; end I=1; N=10; while I<=N J=1; while J<=N A(I,J)=1/(I+J-1); J=J+1; end I=I+1; end »while_examp Similar to other programming languages Repeats loop until logical condition returns FALSE. Can be nested.

11 Copyright  by The MathWorks, Inc. Programming - 11 Introduction to M ATLAB Recall: Array Operations Using Array Operations: Using Loops: [rows, cols] = size(M); for I = 1:rows for J = 1:cols Density(I,J) = M(I,J)/(L(I,J)*W(I,J)*H(I,J)); end [rows, cols] = size(M); for I = 1:rows for J = 1:cols Density(I,J) = M(I,J)/(L(I,J)*W(I,J)*H(I,J)); end Density = Mass(I,J)/(Length.*Width.*Height); »array_vs_loops

12 Copyright  by The MathWorks, Inc. Programming - 12 Introduction to M ATLAB EVAL Command % This file creates the first N magic matrices. % Each matrix is saved as a variable: "magic#". N = 10; for I = 1:N eval(['magic', num2str(I), ' = magic(I)']); end % This file creates the first N magic matrices. % Each matrix is saved as a variable: "magic#". N = 10; for I = 1:N eval(['magic', num2str(I), ' = magic(I)']); end »eval_examp Evaluates the MATLAB expression specified by the input string. Very useful for inserting indices into strings.

13 Copyright  by The MathWorks, Inc. Programming - 13 Introduction to M ATLAB Exercise: Script M-files Write a script file to monitor process variation: Load data: >> data = load('script_data.txt'); (M-by-N process data matrix - M parts per shift, N shifts) For each shift: Calculate the mean & standard deviation. Save the data, mean & SD to the workspace. (Use a separate variable for each shift: data1, data2,...) Plot the data in a new figure window. Plot lines showing the mean and up to +/- 3 STD. Annotate the figure appropriately.

14 Copyright  by The MathWorks, Inc. Programming - 14 Introduction to M ATLAB Results: Script M-files

15 Copyright  by The MathWorks, Inc. Programming - 15 Introduction to M ATLAB Solution: Script M-files [parts, shifts]=size(data); for I=1:shifts DATA = data(:,I); MEAN = mean(DATA); % Calculating mean & Std. deviation STDEV = std(DATA); figure(I); clf; hold on % Creating plots plot(1:parts, DATA, 'b'); plot([0 parts], [0 0], 'k:',... [0 parts], [1 1]*MEAN, 'r-.',... [0 parts], [1 1]*(MEAN-STDEV), 'r:',... [0 parts], [1 1]*(MEAN+STDEV), 'r:',... ); %.....etc. % Writing variables to workspace eval(['data', num2str(I), '=data(:,I);']); eval(['mean', num2str(I), '=means(I);']); eval(['stdev', num2str(I), '=stdev(I);']); end [parts, shifts]=size(data); for I=1:shifts DATA = data(:,I); MEAN = mean(DATA); % Calculating mean & Std. deviation STDEV = std(DATA); figure(I); clf; hold on % Creating plots plot(1:parts, DATA, 'b'); plot([0 parts], [0 0], 'k:',... [0 parts], [1 1]*MEAN, 'r-.',... [0 parts], [1 1]*(MEAN-STDEV), 'r:',... [0 parts], [1 1]*(MEAN+STDEV), 'r:',... ); %.....etc. % Writing variables to workspace eval(['data', num2str(I), '=data(:,I);']); eval(['mean', num2str(I), '=means(I);']); eval(['stdev', num2str(I), '=stdev(I);']); end »script_soln (uses: script_data.txt)

16 Copyright  by The MathWorks, Inc. Programming - 16 Introduction to M ATLAB Functions Core MATLAB (Built-in) Functions sin, abs, exp,... MATLAB-supplied M-file Functions mean, stat, … User-created M-file Functions ????? Differences between Script & Function M-files: Structural Syntax Function Workspaces, Inputs & Outputs

17 Copyright  by The MathWorks, Inc. Programming - 17 Introduction to M ATLAB function y = mean(x) % MEAN Average or mean value. % For vectors, MEAN(x) returns the mean value. % For matrices, MEAN(x) is a row vector % containing the mean value of each column. [m,n] = size(x); if m == 1 m = n; end y = sum(x)/m; function y = mean(x) % MEAN Average or mean value. % For vectors, MEAN(x) returns the mean value. % For matrices, MEAN(x) is a row vector % containing the mean value of each column. [m,n] = size(x); if m == 1 m = n; end y = sum(x)/m; Structure of a Function M-file Keyword: functionFunction Name (same as file name.m) Output Argument(s)Input Argument(s) Online Help MATLAB Code »output_value = mean(input_value) Command Line Syntax

18 Copyright  by The MathWorks, Inc. Programming - 18 Introduction to M ATLAB Multiple Input & Output Arguments function r = ourrank(X,tol) % OURRANK Rank of a matrix s = svd(X); if (nargin == 1) tol = max(size(X))*s(1)*eps; end r = sum(s > tol); function r = ourrank(X,tol) % OURRANK Rank of a matrix s = svd(X); if (nargin == 1) tol = max(size(X))*s(1)*eps; end r = sum(s > tol); function [mean,stdev] = ourstat(x) % OURSTAT Mean & std. deviation [m,n] = size(x); if m == 1 m = n; end mean = sum(x)/m; stdev = sqrt(sum(x.^2)/m – mean.^2); function [mean,stdev] = ourstat(x) % OURSTAT Mean & std. deviation [m,n] = size(x); if m == 1 m = n; end mean = sum(x)/m; stdev = sqrt(sum(x.^2)/m – mean.^2); Multiple Input Arguments (, ) Multiple Output Arguments [, ] »RANK = ourrank(rand(5),0.1); »[MEAN,STDEV] = ourstat(1:99);

19 Copyright  by The MathWorks, Inc. Programming - 19 Introduction to M ATLAB Workspaces 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.)

20 Copyright  by The MathWorks, Inc. Programming - 20 Introduction to M ATLAB Global Workspace Function Workspace Inter-Workspace Communication Function inputs and outputs Global variables (AVOID THESE) MATLAB 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.

21 Copyright  by The MathWorks, Inc. Programming - 21 Introduction to M ATLAB Tips for using Global Variables DON’T USE THEM If you absolutely must use them: Avoid name conflicts whos global clear global isglobal()

22 Copyright  by The MathWorks, Inc. Programming - 22 Introduction to M ATLAB Exercise: Function M-files Let’s go back to the process monitoring exercise: Start with your script file (or the given solution) >> edit script_soln Create a function which replicates as much of the code inside the for loop as possible. (NOTE: It may not make sense to replace everything) Now modify your script file to call your function. Run your new script file and compare the results.

23 Copyright  by The MathWorks, Inc. Programming - 23 Introduction to M ATLAB Results: Function M-files

24 Copyright  by The MathWorks, Inc. Programming - 24 Introduction to M ATLAB Solution: Function M-files (1) % Modified Script file % ==================== % This solution sets the figure#, overwrites the title, & % writes the workspace variables outside the function. shifts=size(data,2); for I=1:shifts DATA = data(:,I); figure(I) % Function Call [MEAN, STDEV] = func_plot(DATA); % Writing variables to workspace eval(['data', num2str(I), '=DATA;']); eval(['mean', num2str(I), '=MEAN;']); eval(['stdev', num2str(I), '=STDEV;']); end % Modified Script file % ==================== % This solution sets the figure#, overwrites the title, & % writes the workspace variables outside the function. shifts=size(data,2); for I=1:shifts DATA = data(:,I); figure(I) % Function Call [MEAN, STDEV] = func_plot(DATA); % Writing variables to workspace eval(['data', num2str(I), '=DATA;']); eval(['mean', num2str(I), '=MEAN;']); eval(['stdev', num2str(I), '=STDEV;']); end »func_soln(uses: func_plot & script_data.txt)

25 Copyright  by The MathWorks, Inc. Programming - 25 Introduction to M ATLAB Solution: Function M-files (2) function [MEAN, STDEV] = func_plot(data) % FUNC_PLOT Calculates mean & std. deviation & plots data DATA = data(:); parts= length(DATA); MEAN = mean(DATA); % Calculating mean & Std. deviation STDEV = std(DATA); clf; hold on% Creating plots plot(1:parts, DATA, 'b'); plot([0 parts], [0 0], 'k:',... [0 parts], [1 1]*MEAN, 'r-.',... [0 parts], [1 1]*(MEAN-STDEV), 'r:',... [0 parts], [1 1]*(MEAN+STDEV), 'r:',... ); %.....etc. xlabel('Part Number'); ylabel('Deviation from Spec. (mm)'); function [MEAN, STDEV] = func_plot(data) % FUNC_PLOT Calculates mean & std. deviation & plots data DATA = data(:); parts= length(DATA); MEAN = mean(DATA); % Calculating mean & Std. deviation STDEV = std(DATA); clf; hold on% Creating plots plot(1:parts, DATA, 'b'); plot([0 parts], [0 0], 'k:',... [0 parts], [1 1]*MEAN, 'r-.',... [0 parts], [1 1]*(MEAN-STDEV), 'r:',... [0 parts], [1 1]*(MEAN+STDEV), 'r:',... ); %.....etc. xlabel('Part Number'); ylabel('Deviation from Spec. (mm)'); »func_soln(uses: func_plot & script_data.txt)

26 Copyright  by The MathWorks, Inc. Programming - 26 Introduction to M ATLAB Subfunctions Allows more than one function to be within the same M-file (modularize code) M-file must have the name of the first (primary) function Subfunctions can only be called from within the same M-file Each subfunction has its own workspace

27 Copyright  by The MathWorks, Inc. Programming - 27 Introduction to M ATLAB Example: Subfunctions function [totalsum,average] = subfunc (input_vector) % SUBFUNC Calculates cumulative total & average totalsum = sum(input_vector); average = ourmean(input_vector); %Call to subfunction function y = ourmean(x) % (OURMEAN) Calculates average [m,n] = size(x); if m == 1 m = n; end y = sum(x)/m; function [totalsum,average] = subfunc (input_vector) % SUBFUNC Calculates cumulative total & average totalsum = sum(input_vector); average = ourmean(input_vector); %Call to subfunction function y = ourmean(x) % (OURMEAN) Calculates average [m,n] = size(x); if m == 1 m = n; end y = sum(x)/m; »[SUM, MEAN] = subfunc(rand(1,50)) Primary Function Sub- Function

28 Copyright  by The MathWorks, Inc. Programming - 28 Introduction to M ATLAB Private Functions Reside in a subdirectory named "private" Only accessible to functions in parent directory Only accessible to functions in parent directory. private directory

29 Copyright  by The MathWorks, Inc. Programming - 29 Introduction to M ATLAB MATLAB Calling Priority High variable built-in function subfunction private function MEX-file P-file M-file Low » cos='This string.'; » cos(8) ans = r » clear cos » cos(8) ans = » cos='This string.'; » cos(8) ans = r » clear cos » cos(8) ans =

30 Copyright  by The MathWorks, Inc. Programming - 30 Introduction to M ATLAB Visual Debugging Set Breakpoint Clear Breaks Step In Single Step Continue Quit Debugging »[SUM, MEAN] = subfunc(rand(1,50)) Select Workspace Set Auto- Breakpoints

31 Copyright  by The MathWorks, Inc. Programming - 31 Introduction to M ATLAB Example: Visual Debugging Set up your debugger to stop if an error occurs Then run: »[SUM, MEAN] = subfunc_error(rand(1,50))

32 Copyright  by The MathWorks, Inc. Programming - 32 Introduction to M ATLAB Example: Visual Debugging (2) Editor/Debugger opens the relevant file and identifies the line where the error occurred. Current Location Current Workspace (Function)

33 Copyright  by The MathWorks, Inc. Programming - 33 Introduction to M ATLAB Example: Visual Debugging (3) Error message Access to Function’s Workspace Debug Mode

34 Copyright  by The MathWorks, Inc. Programming - 34 Introduction to M ATLAB Section Summary Script Files Flow Control & Array Operations EVAL Command Functions Structural Syntax Variables & Workspaces Subfunctions and Private Functions Visual Debugging


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