Introduction to MATLAB Damon Tomlin February 22, 2008 Lecture 3: Data Visualization & User Interfaces

A quick word about SPM... This can be a little intimidating...

“Any sufficiently advanced technology is indistinguishable from magic.” SPM is three things: – –Some functions that work on numbers (your data) – –Some functions that display the crunched numbers – –A bunch of buttons that run the functions when you press them -- Arthur C. Clarke, possibly describing SPM

Overview of MATLAB Graphics FiguresAxes UI Objects Handles –If you can see it, it has a handle. –Some things you can’t see have handles, too. –Use handles to manipulate properties.

Handles & Properties Figures, axes, and graphics have handles, just like files These objects have properties These properties can be altered

How many ways can we look at data? 2D line plots Pseudocolor Images Histograms 3D shapes

2D Plots plot(x,y); plot([x1 x2 x3],[y1 y2 y3]); plot(x1,y1,’r.’,x2,y2,’b-’);

Images imagesc –Pseudocolor –Colormaps image –M x N x 3 matrix

Histograms hist –designate bins bar –generic bar graph

3D Visualization Surface plots –Color –Transparency Mesh plots 3D shapes

Making Visualizations More Informative xlabel, ylabel, zlabel titlelegend

Other handy functions subplot(rows,columns,number) Axis([xmin xmax ymin max]) set(handle,’PropertyName’,value,...); get(handle,’PropertyName’)

What’s a Graphical User Interface? (GUI) Figure windows Buttons, menus, sliders, etc. Appearance changes depending on inputs & outputs Eliminates command line typing

Demystifying GUI’s Interface objects have properties –Style – type of object –String – text associated with object –Callback – what the object does –Value – current value of object What these properties mean depends on the type (Style) of object created

UI Styles: Buttons Buttons cause commands to be executed Style – pushbutton String – text on the button Callback – string containing command(s) executed by button Value – not important

The Eval Function Executes a string as though it were a command typed into a command window or function Example 1: eval(‘disp(a);’); Example 2: eval([‘save ‘ FileName ‘ a b;’]);

Callbacks and Eval Callbacks are assigned within functions Callbacks are executed outside functions –(usually) Therefore, any variables a callback needs have to be stored somehow.

UI Styles: Radio Buttons Style – radiobutton String – text on the button Value – whether button is pushed in or out Callback – exclusivity code & additional functions Used in sets for mutually exclusive, boolean options

UI Styles: Check Boxes Style – checkbox String – text on the box Value – whether button is checked Callback – often nothing, unless switching the option’s value executes a function Used for boolean options

UI Styles: Edit Windows Style – edit String – text in the box Value – not used Callback – function executed when Enter key is pressed Used for typed inputs of names & values

UI Styles: Slider Bars Style – slider String – not used Value – position of slider – between Max and Min Callback – function executed when slider is moved Used when a variable can take on a spectrum of values

UI Styles: Text Boxes Style – text String – text in the box Value – not used Callback – not used Used for displaying information, entitling portions of a GUI

UI Styles: Frames Style – Frame String – not used Value – not used Callback – not used Used for grouping other objects visually

UI Styles: List Boxes Style – listbox String – cell array of each possible choice Value – currently highlighted selection Callback – function executed when an item is selected Used for selecting options when their names and numbers may change

UI Styles: Pop Up Menus Style – popupmenu String – cell array of each possible choice Value – currently selected option Callback – function executed when an item is selected Used for selecting options in a more compact manner

Useful Functions set – change something’s properties get – find out what something’s properties guidata – attach data to/pull data from GUI

Summary MATLAB has lots of functions to help you look at your data You can connect functions to GUI’s so you don’t have to type as much As we’ll see, this is exactly what SPM does.