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Programming in MATLAB

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

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Programming in MATLAB

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

  2. 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 Syllabus

  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. A brief discussion of matrices 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) First line is function declaration local variables: x, n, mean, stdev output: mean stdev input: x 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 Reminder: clear – clears workspace clc – clears command window Hint: right-click on heading area to choose information to display

  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). You can import any of these file formats (except XLSB, XLSM, HDF5, and platform-specific video) using the Import Wizard or the importdata function. Third-party software is available for netCDF files in older versions of MATLAB

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

  21. File I/O Example • readField.m

  22. Questions?

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