Introduction to MATLAB
Programming
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Introduction to MATLAB
Programming - 2
Section Outline
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Script Files
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Flow Control & Array Operations
EVAL Command
Functions
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Structural Syntax
Variables & Workspaces
Subfunctions and Private Functions
Visual Debugging
Copyright  1984 - 1998 by The MathWorks, Inc.
Introduction to MATLAB
Programming - 3
The MATLAB Path
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MATLAB Path:
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List of directories searched by MATLAB.
(Includes \toolbox directories)
Path Cache:
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List of \toolbox files & locations.
Created at startup to increase speed.
Only updated when PATH command is called.
Working with the Path:
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Path Browser (PATHTOOL)
PATH, ADDPATH, RMPATH
Copyright  1984 - 1998 by The MathWorks, Inc.
Introduction to MATLAB
Programming - 4
MATLAB Editor/Debugger
»edit <filename>
Copyright  1984 - 1998 by The MathWorks, Inc.
Introduction to MATLAB
Programming - 5
Script M-files
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Standard ASCII text files
Contain a series of MATLAB expressions
(Typed as you would at the command line)
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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.
Copyright  1984 - 1998 by The MathWorks, Inc.
Introduction to MATLAB
Programming - 6
Flow Control Constructs
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Logic Control:
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IF / ELSEIF / ELSE
SWITCH / CASE / OTHERWISE
Iterative Loops:
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FOR
WHILE
Copyright  1984 - 1998 by The MathWorks, Inc.
Introduction to MATLAB
Programming - 7
The if, elseif and else statements
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Works on Conditional
statements
if I == J
Short-circuited in
MATLAB - once a
condition is true, the
sequence terminates.
elseif abs(I-J) == 1
A(I,J) = 2;
A(I,J) = -1;
else
A(I,J) = 0;
end
»if_examp
Copyright  1984 - 1998 by The MathWorks, Inc.
Introduction to MATLAB
Programming - 8
Switch, Case, and Otherwise
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More efficient than elseif
statements
Only the first matching
case is executed
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_examp
Copyright  1984 - 1998 by The MathWorks, Inc.
Introduction to MATLAB
Programming - 9
The for loop
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Similar to other
programming languages
Repeats loop a set
number of times (based
on index)
Can be nested
N=10;
for I = 1:N
for J = 1:N
A(I,J) = 1/(I+J-1);
end
end
»for_examp
Copyright  1984 - 1998 by The MathWorks, Inc.
Introduction to MATLAB
Programming - 10
The while loop
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Similar to other
programming languages
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Repeats loop until logical
condition returns FALSE.
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Can be nested.
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
Copyright  1984 - 1998 by The MathWorks, Inc.
Introduction to MATLAB
Programming - 11
Recall: Array Operations
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Using Array Operations:
Density = Mass(I,J)/(Length.*Width.*Height);
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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
»array_vs_loops
Copyright  1984 - 1998 by The MathWorks, Inc.
Introduction to MATLAB
Programming - 12
EVAL Command
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Evaluates the MATLAB expression specified by
the input string.
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Very useful for inserting indices into strings.
% 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
Copyright  1984 - 1998 by The MathWorks, Inc.
Introduction to MATLAB
Programming - 13
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)
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For each shift:
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Calculate the mean & standard deviation.
Save the data, mean & SD to the workspace.
(Use a separate variable for each shift: data1, data2, ...)
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Plot the data in a new figure window.
Plot lines showing the mean and up to +/- 3 STD.
Annotate the figure appropriately.
Copyright  1984 - 1998 by The MathWorks, Inc.
Introduction to MATLAB
Programming - 14
Results: Script M-files
Copyright  1984 - 1998 by The MathWorks, Inc.
Introduction to MATLAB
Programming - 15
Solution: Script M-files
[parts, shifts]=size(data);
for I=1:shifts
DATA = data(:,I);
MEAN = mean(DATA);
STDEV = std(DATA);
% Calculating mean & Std. deviation
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)
Copyright  1984 - 1998 by The MathWorks, Inc.
Introduction to MATLAB
Programming - 16
Functions
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Core MATLAB (Built-in) Functions
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sin, abs, exp, ...
MATLAB-supplied M-file Functions
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mean, stat, …
User-created M-file Functions
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?????
Differences between Script & Function M-files:
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Structural Syntax
Function Workspaces, Inputs & Outputs
Copyright  1984 - 1998 by The MathWorks, Inc.
Introduction to MATLAB
Programming - 17
Structure of a Function M-file
Keyword: function
Function Name (same as file name .m)
Output Argument(s)
Input Argument(s)
function y = mean(x)
% MEAN Average or mean value.
Online Help
% 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);
MATLAB
Code
if m == 1
m = n;
end
y = sum(x)/m;
»output_value = mean(input_value)
Command Line Syntax
Copyright  1984 - 1998 by The MathWorks, Inc.
Introduction to MATLAB
Programming - 18
Multiple Input & Output Arguments
function r = ourrank(X,tol)
% OURRANK Rank of a matrix
Multiple Input
Arguments ( , )
s = svd(X);
if (nargin == 1)
tol = max(size(X))*s(1)*eps;
Multiple Output
Arguments [ , ]
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);
»RANK = ourrank(rand(5),0.1);
»[MEAN,STDEV] = ourstat(1:99);
Copyright  1984 - 1998 by The MathWorks, Inc.
Introduction to MATLAB
Programming - 19
Workspaces in MATLAB
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MATLAB (or Base) Workspace:
For command line and script file variables.
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Function Workspaces:
Each function has its own workspace for local variables.
Communicate to Function Workspace via inputs & outputs.
(Promotes structured coding & prevents name conflicts.)
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Global Workspace:
Global variables can be shared by multiple workspaces.
(Must be initialized in all relevant workspaces.)
Copyright  1984 - 1998 by The MathWorks, Inc.
Introduction to MATLAB
Programming - 20
Inter-Workspace Communication
Function inputs
and outputs
Global variables
(AVOID THESE)
Initialize global variables in
all relevant workspaces:
»global variable_name
MATLAB
Workspace
Function
Workspace
Global
Workspace
Initialize global variables in
the “source” workspace
before referring to them
from other workspaces.
Copyright  1984 - 1998 by The MathWorks, Inc.
Introduction to MATLAB
Programming - 21
Tips for using Global Variables
• DON’T USE THEM
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If you absolutely must use them:
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Avoid name conflicts
whos global
clear global
isglobal()
Copyright  1984 - 1998 by The MathWorks, Inc.
Introduction to MATLAB
Programming - 22
Exercise: Function M-files
Let’s go back to the process monitoring exercise:
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Start with your script file (or the given solution)
>> edit script_soln
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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)
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Now modify your script file to call your function.
Run your new script file and compare the results.
Copyright  1984 - 1998 by The MathWorks, Inc.
Introduction to MATLAB
Programming - 23
Results: Function M-files
Copyright  1984 - 1998 by The MathWorks, Inc.
Introduction to MATLAB
Programming - 24
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
»func_soln
(uses: func_plot & script_data.txt)
Copyright  1984 - 1998 by The MathWorks, Inc.
Introduction to MATLAB
Programming - 25
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);
STDEV = std(DATA);
% Calculating mean & Std. deviation
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)
Copyright  1984 - 1998 by The MathWorks, Inc.
Introduction to MATLAB
Programming - 26
Subfunctions
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Allows more than one function to be within the
same M-file (modularize code)
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M-file must have the name of the first (primary)
function
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Subfunctions can only be called from within the
same M-file
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Each subfunction has its own workspace
Copyright  1984 - 1998 by The MathWorks, Inc.
Introduction to MATLAB
Programming - 27
Example: Subfunctions
function [totalsum,average] = subfunc (input_vector)
Primary
Function
% SUBFUNC Calculates cumulative total & average
totalsum = sum(input_vector);
average = ourmean(input_vector);
%Call to subfunction
function y = ourmean(x)
% (OURMEAN) Calculates average
SubFunction
[m,n] = size(x);
if m == 1
m = n;
end
y = sum(x)/m;
»[SUM, MEAN] = subfunc(rand(1,50))
Copyright  1984 - 1998 by The MathWorks, Inc.
Introduction to MATLAB
Programming - 28
Private Functions
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private
directory
Reside in a subdirectory named "private"
Only accessible to functions in parent directory
Only accessible
to functions in
parent directory.
Copyright  1984 - 1998 by The MathWorks, Inc.
Introduction to MATLAB
Programming - 29
MATLAB Calling Priority
High
variable
built-in function
subfunction
private function
MEX-file
P-file
» cos='This string.';
» cos(8)
ans =
r
» clear cos
» cos(8)
ans =
-0.1455
M-file
Low
Copyright  1984 - 1998 by The MathWorks, Inc.
Introduction to MATLAB
Programming - 30
Visual Debugging
Select
Workspace
Set AutoBreakpoints
Set Breakpoint
Clear Breaks
Step In
Single Step
Continue
Quit Debugging
»[SUM, MEAN] = subfunc(rand(1,50))
Copyright  1984 - 1998 by The MathWorks, Inc.
Introduction to MATLAB
Programming - 31
Example: Visual Debugging
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Set up your debugger to stop if an error occurs
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Then run:
»[SUM, MEAN] = subfunc_error(rand(1,50))
Copyright  1984 - 1998 by The MathWorks, Inc.
Introduction to MATLAB
Programming - 32
Example: Visual Debugging (2)
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Current
Location
Editor/Debugger opens the relevant file and
identifies the line where the error occurred.
Current
Workspace
(Function)
Copyright  1984 - 1998 by The MathWorks, Inc.
Introduction to MATLAB
Programming - 33
Example: Visual Debugging (3)
Error message
Debug
Mode
Access to
Function’s
Workspace
Copyright  1984 - 1998 by The MathWorks, Inc.
Introduction to MATLAB
Programming - 34
Section Summary
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Script Files
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Flow Control & Array Operations
EVAL Command
Functions
•
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Structural Syntax
Variables & Workspaces
Subfunctions and Private Functions
Visual Debugging
Copyright  1984 - 1998 by The MathWorks, Inc.