Introduction to M ATLAB Programming .

Introduction to MATLAB

Programming

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Copyright 1984 - 1998 by The MathWorks, Inc.

Programming - 2Introduction to MATLAB

Section Outline

• Script Files

• Flow Control & Array Operations

• EVAL Command

• Functions

• Structural Syntax

• Variables & Workspaces

• Subfunctions and Private Functions

• Visual Debugging



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



MATLAB Editor/Debugger

»edit <filename>



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.



Flow Control Constructs

• Logic Control:

• IF / ELSEIF / ELSE

• SWITCH / CASE / OTHERWISE

• Iterative Loops:

• FOR

• WHILE



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.



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



• 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

end

N=10;

for I = 1:N

for J = 1:N

A(I,J) = 1/(I+J-1);

end

end

»for_examp



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;

endI=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;

endI=I+1;

end

»while_examp

• Similar to other programming languages

• Repeats loop until logical condition returns FALSE.

• Can be nested.



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

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

end

Density = Mass(I,J)/(Length.*Width.*Height);Density = Mass(I,J)/(Length.*Width.*Height);

»array_vs_loops



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.



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.



Results: Script M-files



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)



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:


• Function Workspaces, Inputs & Outputs



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-fileKeyword: function Function Name (same as file name .m)

Output Argument(s) Input Argument(s)

Online Help

MATLABCode

»output_value = mean(input_value) Command Line Syntax



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;endmean = 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;endmean = 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);



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.)



GlobalWorkspace

FunctionWorkspace

Inter-Workspace Communication

Function inputs

and outputs

Global variables

(AVOID THESE)

MATLABWorkspace

Initialize global variables in all relevant workspaces:»global variable_name

Initialize global variables in the “source” workspace before referring to them from other workspaces.



Tips for using Global Variables

• DON’T USE THEM

• If you absolutely must use them:

• Avoid name conflicts

• whos global

• clear global

• isglobal()



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.



Results: Function M-files



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)



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. deviationSTDEV = std(DATA);

clf; hold on % Creating plotsplot(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. deviationSTDEV = std(DATA);

clf; hold on % Creating plotsplot(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)



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



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))

PrimaryFunction

Sub-Function



Private Functions

• Reside in a subdirectory named "private"

• Only accessible to functions in parent directory

Only accessible to functions inparent directory.

privatedirectory



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 =

-0.1455

» cos='This string.';

» cos(8)

ans =

r

» clear cos

» cos(8)

ans =

-0.1455



Visual Debugging

Set BreakpointClear BreaksStep InSingle StepContinueQuit Debugging

»[SUM, MEAN] = subfunc(rand(1,50))

Select Workspace

Set Auto-Breakpoints



Example: Visual Debugging

• Set up your debugger to stop if an error occurs

• Then run: »[SUM, MEAN] = subfunc_error(rand(1,50))



Example: Visual Debugging (2)

• Editor/Debugger opens the relevant file and identifies the line where the error occurred.

CurrentLocation Current

Workspace (Function)



Example: Visual Debugging (3)

Error messageError message

Access to Function’s Workspace

Access to Function’s WorkspaceDebug

ModeDebug Mode



Section Summary

• Script Files

• Flow Control & Array Operations

• EVAL Command

• Functions


• Variables & Workspaces

• Subfunctions and Private Functions

• Visual Debugging

Introduction to M ATLAB Programming .

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