What is your favourite MATLAB/Octave programming trick? [closed]

Answer 1

Using xlim and ylim to draw vertical and horizontal lines. Examples:

1. Draw a horizontal line at y=10:

   line(xlim, [10 10])

2. Draw vertical line at x=5:

   line([5 5], ylim)

Answer 2

cellfun and arrayfun for automated for loops.

Answer 3

In order to be able to quickly test a function, I use nargin like so:

function result = multiply(a, b)
if nargin == 0 %no inputs provided, run using defaults for a and b
    clc;
    disp('RUNNING IN TEST MODE')
    a = 1;
    b = 2;
end

result = a*b;

Later on, I add a unit test script to test the function for different input conditions.

Answer 4

Executing a Simulink model directly from a script (rather than interactively) using the sim command. You can do things like take parameters from a workspace variable, and repeatedly run sim in a loop to simulate something while varying the parameter to see how the behavior changes, and graph the results with whatever graphical commands you like. Much easier than trying to do this interactively, and it gives you much more flexibility than the Simulink "oscilloscope" blocks when visualizing the results. (although you can't use it to see what's going on in realtime while the simulation is running)

A really important thing to know is the DstWorkspace and SrcWorkspace options of the simset command. These control where the "To Workspace" and "From Workspace" blocks get and put their results. Dstworkspace defaults to the current workspace (e.g. if you call sim from inside a function the "To Workspace" blocks will show up as variables accessible from within that same function) but SrcWorkspace defaults to the base workspace and if you want to encapsulate your call to sim you'll want to set SrcWorkspace to current so there is a clean interface to providing/retrieving simulation input parameters and outputs. For example:

function Y=run_my_sim(t,input1,params)
% runs "my_sim.mdl" 
% with a From Workspace block referencing I1 as an input signal
% and parameters referenced as fields of the "params" structure
% and output retrieved from a To Workspace block with name O1.
opt = simset('SrcWorkspace','current','DstWorkspace','current');
I1 = struct('time',t,'signals',struct('values',input1,'dimensions',1));
Y = struct;
Y.t = sim('my_sim',t,opt);
Y.output1 = O1.signals.values;

Answer 5

-You can make a Matlab shortcut to an initialization file called startup.m. Here, I define formatting, precision of the output, and plot parameters for my Matlab session (for example, I use a larger plot axis/font size so that .fig's can be seen plainly when I put them in presentations.) See a good blog post from one of the developers about it http://blogs.mathworks.com/loren/2009/03/03/whats-in-your-startupm/ .

-You can load an entire numerical ascii file using the "load" function. This isn't particularly fast, but gets the job done quickly for prototyping (shouldn't that be the Matlab motto?)

-As mentioned, the colon operator and vectorization are lifesavers. Screw loops.

Answer 6

Provide quick access to other function documentation by adding a "SEE ALSO" line to the help comments. First, you must include the name of the function in all caps as the first comment line. Do your usual comment header stuff, then put SEE ALSO with a comma separated list of other related functions.

function y = transmog(x)
%TRANSMOG Transmogrifies a matrix X using reverse orthogonal eigenvectors
%
% Usage:
%   y = transmog(x)
%
% SEE ALSO
% UNTRANSMOG, TRANSMOG2

When you type "help transmog" at the command line, you will see all the comments in this comment header, with hyperlinks to the comment headers for the other functions listed.