Download Matlab Advanced Programming: Strengths, Weaknesses, Scripts vs. Functions, and Guidelines and more Study notes Electrical and Electronics Engineering in PDF only on Docsity! Matlab Advanced Programming Matt Wyant University of Washington Matlab as a programming Language – Strengths (as compared to C/C++/Fortran) • Fast to write -no type declarations needed • Memory allocation/deallocation handled automatically • Functions and scripts can be accessed automatically from path • Vector/Matrix operations in many dimensions built in • Polymorphic with respect to matrix dimensions Outline • Scripts vs. Functions • Techniques for writing functions • Structures • Cell-Arrays • Examples Not included • Matlab graphics • Object-oriented programming • Interfaces to other languages • Not much on handling matrices Matlab Scripts plotsquared.m: x = [-5:5]; y = x .^2; plot(x,y) Run with ‘plotsquared’ Ways to protect against scope problems in scripts • clear all – include at top of script or type it – sometimes not desirable • Initialize all variables you use • Beware assignment to parts of an un- initialized array Suppose y is a 20x20 array. Then the following script is run: x = [-5:5]; y(1:11) = x .^2; plot(x,y) Fixed version: y = zeros(1:11) x = [-5:5]; y(1:11) = x .^2; plot(x,y) Disadvantages of Functions • Designing them takes time and practice. • Debugging can be more involved than for scripts. Guidelines for writing functions • Write at least minimal documentation – required inputs – optional inputs – outputs – units • Use a descriptive function name • Use descriptive variable names • Possibly check the input arguments – size – number of dimensions – type Guidelines for writing functions • If you can, don’t assume the size of input matrices • Write functions to apply a process to whole matrices, not just scalars (avoid looping over matrices). • If you see repeated similar procedures, consider looping over them or making them a function. • If you can, don’t assume the size of input matrices • Avoid GLOBAL variables. – Make them arguments instead. – If you need persistent variables use ‘persistent’. – If you need lots of physical constants pass them in as a structure) • Small simple functions can be very useful (examples) Cell-arrays • Containers for multiple Matlab objects of different types and sizes • Useful for grouping character strings • Can be used as comma-separated lists • () used to get subset of cell array • {} used to get contents of cells Examples • Exploiting Matlab matrix handling • Passing back complex output using structures • Extending existing Matlab functions using varargin • Looping over variables with cell-arrays Exploiting Matlab matrix handling • Many built-in and user made functions can handle arbitrarily sized matrices. • Matrices typically must all be the same size. • The functions must use element-by-element math methods on these matrices: x .^ y x .* y x ./ y • Example: (qsat.m), (sat_vapor_pressure.m) Looping over variables with cell- arrays Cell-arrays provide a convenient way to loop through variable data (noloop.m, loop.m). References • Matlab Help – help – help [topic] – help [function name] – doc [function name] • www.mathworks.com • Graphics and GUI’s with MATLAB, Patrick Marchand and O. Thomas Holland • This talk will be placed (soon) at ‘www.atmos.washington.edu/~mwyant Additional Topics • Matrix manipulations and higher dimensional matrices • Handle Graphics Techniques • Matlab Graphics for Publication and Presentation • Performance Tips • NetCDF Interface • Handling Missing Data • Interface with C/C++ or Fortran
