# MATLAB Second Seminar - PowerPoint PPT Presentation

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MATLAB Second Seminar. Previous lesson. Last lesson We learnt how to: Interact with MATLAB in the MATLAB command window by typing commands at the command prompt. Define and use variables. Plot graphs.

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MATLAB Second Seminar

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## MATLABSecond Seminar

### Previous lesson

Last lesson We learnt how to:

• Interact with MATLAB in the MATLAB command window by typing commands at the command prompt.

• Define and use variables.

• Plot graphs

It would be nice if you didn't have to manually type these commands at the command prompt whenever you want to use them.

### Problem

• Write a script that asks for a temperature (in degrees Fahrenheit)

• computes the equivalent temperature in degrees Celcius.

• The script should keep running until no number is provided to convert.

• use isempty

### Solution

while 1 % use of an infinite loop

TinF = input('Temperature in F:'); % get input

if isempty(TinF) % how to get out

break

end

TinC = 5*(TinF - 32)/9; % conversion

disp(' ')

disp([' ==> Temperature in C =',num2str(TinC)])

disp(' ')

end

### Functions

• Functions describe subprograms

• Take inputs, generate outputs

• Have local variables (invisible in global workspace)

• Core MATLAB (Built-in) Functions

• sin, abs, exp, ...

Can’t be displayed on screen

• MATLAB-supplied M-file Functions

• mean, linspace, …

Ca be displayed on screen

• User-created M-file Functions

### Core MATLAB (Built-in) Functions

• Elementary built-in functions

• >> help elfun % a list of these functions

• Special Math functions

• >> help specfun

• Special functions - toolboxes

• Each toolbox has a list of special functions that you can use

sin         % Sine.

exp         % Exponential.

abs         % Absolute value. round       % Round towards nearest integer.

lcm         % Least common multiple.

cart2sph    % Transform Cartesian to spherical%coordinates.

Keyword: function

Function Name (same as file name .m)

Output Argument(s)

Input Argument(s)

MATLAB

Code

Command Line Syntax

• output_value = mean(input_value)

### Structure of a Function M-file

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;

### Multiple Input & Output Arguments

Multiple Input Arguments ( , )

functionr = 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);

Multiple Output

Arguments [ , ]

function[mean,stdev] = ourstat(x)

% OURSTAT Mean & std. deviation

[m,n] = size(x);

ifm == 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);

### nargin, nargout, nargchk

• nargin– number of input arguments

- Many of Matlab functions can be run with different number of input variables.

• nargout– number of output arguments

- efficiency

• nargchk – check if number of input arguments is between some ‘low’ and ‘high’ values

### 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.

• Name of Input/output variables can be either equal or different then the variable name in the calling workspace.

• Communicate to Function Workspace via inputs & outputs.

• Global Workspace:

Global variables can be shared by multiple workspaces.

(Must be initialized in all relevant workspaces.)

• 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%shows the contents of the global workspace

>>clear global %erases the variable from both local and global workspaces.

>>isglobal()

### 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

Select Workspace

Set Auto-

Breakpoints

Set Breakpoint

Clear Breaks

Step In

Single Step

Continue

Quit Debugging

### Example: Visual Debugging (2)

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

Current

Location

Current Workspace (Function)

Error message

Debug Mode

### Some Useful MATLAB commands

• whatList all m-files in current directory

• dirList all files in current directory

• lsSame as dir

• type testDisplay test.m in command window

• delete testDelete test.m

• cd a:Change directory to a:

• chdir a:Same as cd

• pwdShow current directory

• which testDisplay current directory path to

test.m

• whyIn case you ever needed a reason

### Problem

• Write a function that asks for a temperature (in degrees Fahrenheit)

• computes the equivalent temperature in degrees Celcius.

• The function should give an error massage in case no number is provided to convert.

• use nargin.

### Solution

functionTinC=temp2(TinF)

TinF = input('Temperature in F:'); % get input

if nargin==0 % if there is no input

disp('no temparture was entered');

TinC=nan;

else

TinC = 5*(TinF - 32)/9; % conversion

disp(' ')

disp([' ==> Temperature in C =',num2str(TinC)])

disp(' ')

end

### MATLAB Input

• if the file is an ascii table, use “load”

• if the file is ascii but not a table, file I/O needs “fopen” and “fclose”

• Reading in data from file using fopen depends on type of data (binary or text)

• Default data type is “binary”

### What Is GUIDE?

• Graphical User Interface Design Environment

• provides a set of tools for creating graphical user interfaces (GUIs).

• GUIDE automatically generates an M-file that controls how the GUI operates.

• Starting GUIDE:

>> guide

OR:

Push buttons

axes

Static text

### GUIDE Tools - The Layout Editor

• In the Quick Start dialog, select the Blank GUI (Default) template

• Display names of components: File preferences Show names in component palette

• Lay out your GUI by dragging components

• (panels, push buttons, pop-up menus, or axes)

• from the component palette, into the layout area

Component panel

Drag to resize

Layout area

### Using the Property Inspector

• Labeling the Buttons

• Select Property Inspector from the View menu.

• Select button by clicking it.

• Fill the name in the String field.

Activate GUI

Property

Inspector

### Programming a GUI

• Callbacks are functions that execute in response to some action by the user.

• A typical action is clicking a push button.

• You program the GUI by coding one or more callbacks for each of its components.

• A GUI's callbacks are found in an M-file that GUIDE generates automatically.

• Callback template for a push button:

### Handles structure

• Save the objects handles: handles.objectname

• Save global data – can be used outside the function.