MATLAB Second Seminar

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MATLABSecond Seminar
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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.
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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

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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(' gt Temperature in C ',num2str(TinC))
  
• disp(' ')
• end

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Functions

• Functions describe subprograms
• Take inputs, generate outputs
• Have local variables (invisible in global
  workspace)
• Core MATLAB (Built-in) Functions
• sin, abs, exp, ...
• Cant be displayed on screen
• MATLAB-supplied M-file Functions
• mean, linspace,
• Ca be displayed on screen
• User-created M-file Functions

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Core MATLAB (Built-in) Functions

• Elementary built-in functions
• gtgt help elfun a list of these functions
•    
• Special Math functions
• gtgt 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.
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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
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Multiple Input Output Arguments
Multiple Input 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 gt tol)

Multiple Output Arguments ,
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(199)

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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

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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.

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Tips for using Global Variables

• DONT USE THEM
• If you absolutely must use them
• Avoid name conflicts
• gtgtwhos global shows the contents of the global
  workspace
• gtgtclear global erases the variable from both
  local and global workspaces.
• gtgtisglobal()

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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
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Visual Debugging
Select Workspace Set Auto- Breakpoints
Set Breakpoint Clear Breaks Step In Single
Step Continue Quit Debugging
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Example Visual Debugging (2)

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

Current Location
Current Workspace (Function)
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Example Visual Debugging (3)
Error message
Access to Functions Workspace
Debug Mode
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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

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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.

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Solution

• function TinCtemp2(TinF)
• TinF input('Temperature in F ') get input
• if nargin0 if there is no input
• disp('no temparture was entered')
• TinCnan
• else
• TinC 5(TinF - 32)/9 conversion
• disp(' ')
• disp(' gt Temperature in C ',num2str(TinC))
  
• disp(' ')
• end

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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

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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
• gtgt guide
• OR

Push buttons
axes
Static text
Pop-up menu
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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
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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
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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

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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