This document provides an introduction to MATLAB programming. It covers topics such as script files, flow control structures, array operations, the EVAL command, functions, variables and workspaces, subfunctions, private functions, and visual debugging. The document consists of 34 pages outlining these MATLAB programming concepts and providing examples to illustrate them.

1. Introduction to MATLAB
Programming
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2. Copyright  1984 - 1998 by The MathWorks, Inc.
Programming - 2
Introduction to MATLAB
Section Outline
• Script Files
• Flow Control & Array Operations
• EVAL Command
• Functions
• Structural Syntax
• Variables & Workspaces
• Subfunctions and Private Functions
• Visual Debugging

3. Copyright  1984 - 1998 by The MathWorks, Inc.
Programming - 3
Introduction to MATLAB
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  1984 - 1998 by The MathWorks, Inc.
Programming - 4
Introduction to MATLAB
MATLAB Editor/Debugger
»edit <filename>

5. Copyright  1984 - 1998 by The MathWorks, Inc.
Programming - 5
Introduction to MATLAB
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.

6. Copyright  1984 - 1998 by The MathWorks, Inc.
Programming - 6
Introduction to MATLAB
Flow Control Constructs
• Logic Control:
• IF / ELSEIF / ELSE
• SWITCH / CASE / OTHERWISE
• Iterative Loops:
• FOR
• WHILE

7. Copyright  1984 - 1998 by The MathWorks, Inc.
Programming - 7
Introduction to MATLAB
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_examp
• Works on Conditional
statements
• Short-circuited in
MATLAB - once a
condition is true, the
sequence terminates.

8. Copyright  1984 - 1998 by The MathWorks, Inc.
Programming - 8
Introduction to MATLAB
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
• More efficient than elseif
statements
• Only the first matching
case is executed
»switch_examp

9. Copyright  1984 - 1998 by The MathWorks, Inc.
Programming - 9
Introduction to MATLAB
• 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
»for_examp

10. Copyright  1984 - 1998 by The MathWorks, Inc.
Programming - 10
Introduction to MATLAB
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
»while_examp
• Similar to other
programming languages
• Repeats loop until logical
condition returns FALSE.
• Can be nested.

11. Copyright  1984 - 1998 by The MathWorks, Inc.
Programming - 11
Introduction to MATLAB
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
Density = Mass(I,J)/(Length.*Width.*Height);
»array_vs_loops

12. Copyright  1984 - 1998 by The MathWorks, Inc.
Programming - 12
Introduction to MATLAB
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
»eval_examp
• Evaluates the MATLAB expression specified by
the input string.
• Very useful for inserting indices into strings.

13. Copyright  1984 - 1998 by The MathWorks, Inc.
Programming - 13
Introduction to MATLAB
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  1984 - 1998 by The MathWorks, Inc.
Programming - 14
Introduction to MATLAB
Results: Script M-files

15. Copyright  1984 - 1998 by The MathWorks, Inc.
Programming - 15
Introduction to MATLAB
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
»script_soln (uses: script_data.txt)

16. Copyright  1984 - 1998 by The MathWorks, Inc.
Programming - 16
Introduction to MATLAB
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  1984 - 1998 by The MathWorks, Inc.
Programming - 17
Introduction to MATLAB
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: function Function 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  1984 - 1998 by The MathWorks, Inc.
Programming - 18
Introduction to MATLAB
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 [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  1984 - 1998 by The MathWorks, Inc.
Programming - 19
Introduction to MATLAB
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  1984 - 1998 by The MathWorks, Inc.
Programming - 20
Introduction to MATLAB
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  1984 - 1998 by The MathWorks, Inc.
Programming - 21
Introduction to MATLAB
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  1984 - 1998 by The MathWorks, Inc.
Programming - 22
Introduction to MATLAB
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  1984 - 1998 by The MathWorks, Inc.
Programming - 23
Introduction to MATLAB
Results: Function M-files

24. Copyright  1984 - 1998 by The MathWorks, Inc.
Programming - 24
Introduction to MATLAB
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)

25. Copyright  1984 - 1998 by The MathWorks, Inc.
Programming - 25
Introduction to MATLAB
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)');
»func_soln (uses: func_plot & script_data.txt)

26. Copyright  1984 - 1998 by The MathWorks, Inc.
Programming - 26
Introduction to MATLAB
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  1984 - 1998 by The MathWorks, Inc.
Programming - 27
Introduction to MATLAB
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;
»[SUM, MEAN] = subfunc(rand(1,50))
Primary
Function
Sub-
Function

28. Copyright  1984 - 1998 by The MathWorks, Inc.
Programming - 28
Introduction to MATLAB
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  1984 - 1998 by The MathWorks, Inc.
Programming - 29
Introduction to MATLAB
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

30. Copyright  1984 - 1998 by The MathWorks, Inc.
Programming - 30
Introduction to MATLAB
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  1984 - 1998 by The MathWorks, Inc.
Programming - 31
Introduction to MATLAB
Example: Visual Debugging
• Set up your debugger to stop if an error occurs
• Then run: »[SUM, MEAN] = subfunc_error(rand(1,50))

32. Copyright  1984 - 1998 by The MathWorks, Inc.
Programming - 32
Introduction to MATLAB
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  1984 - 1998 by The MathWorks, Inc.
Programming - 33
Introduction to MATLAB
Example: Visual Debugging (3)
Error message
Access to
Function’s
Workspace
Debug
Mode

34. Copyright  1984 - 1998 by The MathWorks, Inc.
Programming - 34
Introduction to MATLAB
Section Summary
• Script Files
• Flow Control & Array Operations
• EVAL Command
• Functions
• Structural Syntax
• Variables & Workspaces
• Subfunctions and Private Functions
• Visual Debugging