File Exchange Pick of the Week

November 15th, 2007

Practical example: Algorithm development for making colormaps

In a recent post, I mentioned LazyWeb It worked better than I expected. Matt posted some code that I requested that will highlight a line when you click on it. This works exactly as hoped. Thanks Matt, your MATLAB T-shirt has been shipped to thank you for your effort.

Ned thought this was great, so he posted a request for some code that makes colormaps.

I took up the challenge, mostly so that I could record how I went about developing an algorithm.

I broke this into two videos:

In this first video you will see:

  • The colormaps that we are developing from a journal article
  • The colormap applied to a MATLAB figure
  • How to call the code to make the colormap
  • Explaining the structure of a colormap in MATLAB
  • Exploring colormaps in the colormap editor
  • Plotting a colormap to understand its structure
  • Creating the colormap creating subfunction
  • Testing the subfunction

Find the files here.
PodCast here

In this second video you will see:

  • We review the colormaps that are to be made.
  • Show the four expected calling syntaxes for the function
  • Show how to use VARARGIN to make deal with different numbers of input arguments
  • Show error catching
  • Show different branches of code to be followed based on inputs
  • Developing an algorithm with cell mode to test an algorithm
  • Testing
  • Documentation

Find the files here.
PodCast here

This code was written live, so mistakes were made along the way. This gives you a realistic view of how a MATLAB expert deals with the inevitable errors that occur while programming.

The file that got created is useful on its own, so I have posted it here

Other videos have been gathered here:
http://blogs.mathworks.com/pick/category/video/

Practical example videos have been gathered here:
http://blogs.mathworks.com/pick/category/practical-example

By Doug Hull

14:57 UTC | Posted in PodCast, Practical example, Video | Permalink |

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6 Responses to “Practical example: Algorithm development for making colormaps”

  1. Dan Pace replied on November 19th, 2007 at 09:24 UTC :

    Hi Doug - thanks for the helpful video. I have a question. Is it possible to display two surface plots, with different colormaps, on the same axes? Thanks - Dan

  2. Doug replied on November 19th, 2007 at 10:13 UTC :

    Dan,

    The colormap is a property of the Figure, so all axes in a figure share it.

    Doug

  3. Amir replied on November 20th, 2007 at 01:22 UTC :

    Dan,
    Here is the solution -
    http://www.mathworks.com/support/tech-notes/1200/1215.html
    Amir

  4. Andy replied on December 30th, 2007 at 22:59 UTC :

    Hi Doug - Thank you for creating the very useful makeColorMap. My goal was to integrate this function into my plots that use contourcmap.m. However, I kept getting an error, ‘cmap string must contain a colormap function name’ since contourcmap only allows built in Matlab color maps. My way around this was to comment out lines 64-68 of contourcmap. Do you recommend this solution, and if not, what other methods could I try? Thanks!

  5. Doug replied on January 2nd, 2008 at 11:06 UTC :

    Andy,

    What was the commands you were using? I just tried the example in CONTOURCMAP only I made a throw-away function JETT that just calls JET. This worked fine. Please send or post the code you used and we can figure this out.

    I suspect that my colormap function expects different inputs than CONTOURCMAP gives so things are not working. You will probably want to make a wrapper around my function that takes just a single number input (like JET and other colormap functions do) so that when CONTOURCMAP calls it it will behave like the others.

    Doug

  6. Kika replied on June 26th, 2009 at 14:10 UTC :

    THANK YOU!!
    I’ve been trying to change the colormap but I didn’t know what to do. It was driving me crazy!
    Thank you very much for the help

    Kika

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