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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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Presentation Transcript
previous lesson
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
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
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
  • 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
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.

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

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 & 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, 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
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
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
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

visual debugging
Visual Debugging

Select Workspace

Set Auto-

Breakpoints

Set Breakpoint

Clear Breaks

Step In

Single Step

Continue

Quit Debugging

example visual debugging 2
Example: Visual Debugging (2)
  • Editor/Debugger opens the relevant file and identifies the line where the error occurred.

Current

Location

Current Workspace (Function)

example visual debugging 3
Example: Visual Debugging (3)

Error message

Access to Function’s Workspace

Debug Mode

some useful matlab commands
Some Useful MATLAB commands
  • what List all m-files in current directory
  • dir List all files in current directory
  • ls Same as dir
  • type test Display test.m in command window
  • delete test Delete test.m
  • cd a: Change directory to a:
  • chdir a: Same as cd
  • pwd Show current directory
  • which test Display current directory path to

test.m

  • why In case you ever needed a reason
problem1
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.
solution1
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
MATLAB Input

To read files in

  • 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
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

Pop-up menu

guide tools the layout editor
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
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
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
Handles structure
  • Save the objects handles: handles.objectname
  • Save global data – can be used outside the function.
  • Example: popup menu:
  • Value – user choice of the popup menu
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