Introduction to MATLAB

1. Introduction to MATLAB 3 November 2009

2. Instructor: Andy Newman • Office Hours: Stop by room 306 (main building) whenever • Email: anewman@atmos.colostate.edu • Website: www.atmos.colostate.edu/programming

3. Syllabus • Week 1 (11/03) • Introduction to MATLAB • GUI • Variables, operations, built in functions • Help • Script Files • Week 2 (11/10) • Programming • Syntax • Arrays: Numeric, cell, structure • Strings • Built in functions (i.e. find, mean, max, min, sum, etc) • File I/O (text, binary, netCDF, HDF) • Basic program organization • Debugging

4. Syllabus • Week 3 (11/17) • Graphics • Line, scatter, bar, surface, contour plots, etc • Figure properties (i.e. Axis labels, tick marks) • Colormaps • Saving your plots • Images in MATLAB • Week 4 (12/01) • Somewhat more advanced topics • Making functions • Vectorized code • 3-D plots • Data manipulation in MATLAB: regression, derivatives, others you want… • MATLAB Central File Exchange

5. Syllabus • Week 5 (12/08) • Toolboxes • Mapping • Signal processing • Statistics • Other topics you want to discuss

6. What is MATLAB? • MATLAB is a simple programming language with its own extensive library of mathematical and graphical subroutines • It integrates computation and graphics in one easy to use interface • MATLAB stands for MATrix LABoratory. • MATLAB is very extendable. There are many add-ons (toolboxes) for specific requirements

7. What is MATLAB? • If MATLAB can process and visualize data, why ever use FORTRAN, C, or some other language? • MATLAB is an interpreted language • It is not a compiled language • Therefore identical code executes more slowly, sometimes MUCH more slowly in MATLAB • MATLAB has more memory overhead than equivalent FORTRAN or C programs

8. What is MATLAB? • Main Features • Simple programming rules • Extended accuracy • Continuity among integer, real and complex values • Comprehensive mathematical library • Extensive graphics tools • Linkages with other languages • Transportability across environment • MATLAB scripts will work on PC, UNIX, Mac

9. Starting MATLAB • On UNIX: type matlab at command prompt • Click on the MATLAB icon if you are on a PC • Mac can probably do both… • Issues on startup • MATLAB needs a connection to the license server • Check internet connection • Too many users can use all available licenses • Try again later

10. Starting MATLAB • Once MATLAB is running the GUI (Graphical User Interface) will appear • Default Window apperance

11. Starting MATLAB • Command Window • Main window in MATLAB • Commands entered here

12. Starting MATLAB • MATLAB displays >> prompt when ready for a command • Will have no >> prompt when processing commands • Newer versions also say “Ready” or “Busy” in lower left corner of GUI • Can use arrow keys to work through command history and modify commands • Essentially the same as UNIX command prompt

13. MATLAB GUI • Current Folder Window • Displays contents of the current working directory • MATLAB Search Path • Path that MATLAB uses to search for script and function files • Default path contains all built in MATLAB functions • Can modify path through MATLAB function or going under File>Set Path • MATLAB will ask to modify path if running a program from a folder not in path

14. MATLAB GUI • Workspace Window • Shows all currently defined variables • Array dimensions • Min, max values • Good debugging tool • Command History • Shows all past commands • Can copy and past commands into command window • Double click will execute command

15. MATLAB GUI • Other windows include editor window, figure window, variable editor, help, etc • Will discuss editor and figure window in upcoming weeks, get to help window in a little bit

16. MATLAB GUI • Desktop Menus • File Menu • New • Create new MATLAB program file (m-file) • Open existing m-file • Import data • Set Path • Open recent m-files

17. MATLAB GUI • Edit Menu • Copy, cut, paste • Find and replace phrases • Clear command history, workspace • Desktop Menu • Change appearance of desktop • Select windows to display

18. Interactive Commands • Enter commands at >> prompt • Variable ‘x’ automatically allocated • MATLAB does not require declaration of variables • Nice, but can get you in trouble so be careful

19. Interactive Commands • MATLAB is case sensitive • Variable ‘ans’ will take value of result of command if no equal sign specified • Holds most recent result only • Semicolon at end of line will suppress output, it is not required like in C • Useful in script files and debugging

20. Interactive Commands • Format of output • Defaults to 4 decimal places • Can change using format statement • format long changes output to 15 decimal places

21. Operators • Scalar arithmetic operations Operation MATLAB form • Exponentiation: ^ aba^b • Multiplication: * ab a*b • Right Division: / a / b = a/b a/b • Left Division: \ a \ b = b/a a\b • Addition: + a + b a+b • Subtraction: - a – b a-b • MATLAB will ignore white space between variables and operators

22. Order of Operations • Parentheses • Exponentiation • Multiplication and division have equal precedence • Addition and subtraction have equal precedence • Evaluation occurs from left to right • When in doubt, use parentheses • MATLAB will help match parentheses for you

23. Logical Operators

24. Variables • MATLAB is case sensitive • X is not equal to x • Variable names must start with a letter • You’ll get an error if this doesn’t happen • After that, can be any combination of letters, numbers and underscores • No special characters though

25. Variables • Variable types • Numeric • Logical • Character and string (discussed next week) • Cell and Structure (discussed next week) • Function handle (discussed in week 3)

26. Variables • Don’t name your variables the same as functions • min, max, sqrt, cos, sin, tan, mean, median, etc • Funny things happen when you do this • MATLAB reserved words don’t work either • i, j, eps, nargin, end, pi, date, etc • i, j are reserved as complex numbers initially • Will work as counters in my experience so they can be redefined as real numbers

27. MATLAB Help • Ways to get help in MATLAB • help function name • Provides basic text output • Type helpwin on command line • Look under the help menu on the desktop

28. MATLAB Help • Product help window • Help>product help

29. MATLAB Help • Can browse or search product help for a specific function or topic • MATLAB help has introductory help material, basic overviews of how to use functions, plot, program in MATLAB, example code, etc • lookforkeyword command will also find functions that have the keyword in them • doc function_name brings up the full documentation for the function

30. Resources • Books • Two that seem to be good: • A Concise Introduction to MATLAB by William J. Palm III. 2008, McGraw-Hill, 418 pp. • Essential MATLAB for Engineers and Scientists (Fourth Edition) by Brian Hahn and Dan Valentine. 2010, Academic Press, 480 pp. • Online tutorials and examples are everywhere • Note that older books and tutorials may have options that are no longer available and functions that no longer work • Figures are the prime example

31. Next Week • Arrays • Strings • File I/O • Program layout and debugging

32. Questions?