# Practical example: Algorithm development for making colormaps8

Posted by Doug Hull,

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

Dan Pace replied on : 1 of 8

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

Doug replied on : 2 of 8

Dan,

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

Doug

Andy replied on : 4 of 8

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!

Doug replied on : 5 of 8

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

Kika replied on : 6 of 8

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

Anne-Lene replied on : 7 of 8

Thank you for useful code!

kw replied on : 8 of 8

code is missing. broken url.

These postings are the author's and don't necessarily represent the opinions of MathWorks.