1. Programming in MATLAB Week 14 – 4/28/09 Kate Musgrave kate@atmos.colostate.edu

2. Syllabus Week 13: T 4/21 –Intro to MATLAB –MATLAB GUI –Variables –Operations Week 14: T 4/28 –Functions and scripts –Programming style –Comments –Flow control –File I/O Week 15: T 5/5 –Graphics –Plot types –Figure window –Figure properties –Figures: special topics Week 16: T 5/12 –MATLAB toolboxes –Statistics –Signal processing –Special topics

3. A brief discussion of matrices As mentioned previously, MATLAB is optimized for matrices MATLAB regards all variables as matrices –Scalars are 1x1 matrices –Vectors are 1xn or nx1 matrices –2D matrices are the default, more than 2D are considered multidimensional arrays (nxmxlx…) The class of the matrix is determined by the data type stored within

4. A brief discussion of matrices

5. This is one of the many demos available in MATLAB, which demonstrates basic matrix manipulation.

6. Files used in MATLAB.m files –Both functions and scripts are stored in.m files.mat files –The MATLAB workspace (or specific variables) can be saved in.mat files –These files are easy to save and load, and MATLAB accessing them is very efficient.fig files (next week) –Plots can be saved in.fig files, and then the figure can be edited without reloading data

7. .m files Code can be saved in.m files and run in the command window – exact implementation depends on whether the code is a function or a script

8. Script Simplest kind of m-file Type up a bunch of commands and save as filename.m Type filename in command window to run Example: first_program.m

9. Script Scripts have access to the variables in the workspace, both to read and to write –Changes done to variables in a script will remain after the script is finished Scripts are useful for the automation of repetitive tasks

10. Function Functions are more complex than scripts Functions have their own local variables Functions return output as specified, and can accept input as specified

11. Function Anatomy of a function: function name (must match file name) input: xoutput: mean stdev First line is function declaration local variables: x, n, mean, stdev Examples: stat.m, stat2.m, triDiagMatrix.m, calcERadius.m

12. Commenting Comment your code! Any line starting with % is a comment Comments can be added to the end of existing lines by adding a % –Note that anything after % will be ignored In editor screen comments are green Any comments written at the beginning of an m-file will be displayed by the command help filename

13. Flow control Conditional control – if, else, switch Loop control – for, while, continue, break Program termination – return

14. Conditional control – if, else, elseif if test statement statements elseif test statement statements else statements end Note that ==,~=,>,< are all scalar tests. To test matrices, try: isequal isempty all any

15. Conditional control – switch switch variable or statement case value statements case value statements otherwise statements end Note: the switch statement does not ‘fall through’, only the true case statement will execute.

16. Loop control – for, while for varname = min:max statements end while condition is true statements end Note: continue, break and return -continue skips the remainder of the loop to pass control to the next iteration -break exits from the loop early -similar to break, return exits the program (script or function) early

17. .mat files It is convenient to save your workspace before experimenting with altering variables example: our_vars.mat save filename load filename Hint: right-click on heading area to choose information to display Reminder: clear – clears workspace clc – clears command window

18. File Input/Output Several methods exist in MATLAB depending on the type of file you are trying to read or write Easiest method – the import data wizard –File  Import Data… –Follow on-screen instructions In scripts, use importdata command –help importdata

19. MATLAB File I/O List of file types that MATLAB can read in and write out (version 2009a). Third-party software is available for netCDF files in older versions of MATLAB You can import any of these file formats (except XLSB, XLSM, HDF5, and platform- specific video) using the Import Wizard or the importdata function. Import Wizard importdata

20. MATLAB File I/O Article on importing SDF files (includes importing into MATLAB): http://findarticles.com/p/articles/mi_m0HPJ/is_n6_v44/ai_14823379/pg_4/ Notes on other formats:

21. File I/O Example readField.m

22. Questions?