Create a surface plot with colors associated to value on cell

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Igor de Britto 2011-10-6

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I have a matrix with 3 possible values: 1, 0 and -1. They may contain any combination of those elements. I'd like to choose the colors for each value (like blue for 1, gray for 0 and red for -1).

When I try surface(matrix), it's not possible to differ: surface(ones(X)) surface(zeros(X)) surface(-ones(X))

Any idea on how to get on with it?

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Dr. Seis 2011-10-6

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在 MATLAB Online 中打开

Check out "colormap" in the Matlab Help Navigator. Right under the "Description" section, they talk about creating your own color map. You would define your color map such that the RGB values result in the desired colors to be applied to your surface plot.

Use colormap if you want to choose your own colors...

a=[1 1 -1;0 0 1;-1 -1 1;-1 -1 1];
cmap = [1,0,0;0.5,0.5,0.5;0,0,1]; % 1st row = red; 2nd = gray; 3rd = blue
imagesc(a);
colormap(cmap);

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Igor de Britto 2011-10-11

Thanks a lot, Elige. It works like a charm =) Do you know, however, how can I make the gridlines (something like I would get from a surface or pcolor plot) come out? I tried the caxis command on pcolor, but it does not work.

Dr. Seis 2011-10-14

Does "grid on" work? If so, you may have to play with the settings for "grid"

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Fangjun Jiang 2011-10-6

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在 MATLAB Online 中打开

use pcolor()

Two notes. The last row and last column is not shown so you might want to pad NaNs. Second, pay attention to the image shown. The color on grid (x,y) corresponds to the value in a(x,y). Don't try to map the color with the position of matrix shown in the Command Window. For example:

a=[1 1 -1;0 0 1;-1 -1 1;-1 -1 1];
b=a;
b(end+1,:)=nan;
b(:,end+1)=nan;
pcolor(b);

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Igor de Britto 2011-10-11

@Teja thanks a lot. The axis ij is very useful (was trying to fix it, but it was a minor inconvenience!). However, I'm not having any luck with the set command you suggested.

cmap = [1,0,0;0.5,0.5,0.5;0,0,1]; % 1st row = red; 2nd = gray; 3rd = blue

%I have this matrix

A =

[-1 -1 -1

-1 -1 -1

0 0 0];

pcolor(A)

colormap(cmap);

axis ij; %<--- Flips the image to make it look like the matrix

set(gca,'clim',[-1 1]); %<--- Makes the colors and values match

I'm getting the upper part (-1) as gray and the lowest (0) as blue. I'm posting my whole code so that you may find something missing or messing the plot.

for a = 1:8

h = subplot(4,8,x(a)), pcolor(SIS_tab{a}) ;

xlim([1 Especies]); % limits for X axis

ylim([1 Especies]); % limits for Y axis

axis off; % removes the numbers - thinks of 'xticks []'. Better off like that?

colormap(cmap);

title('Species Interactions'); % title

axis ij; %<--- Flips the image to make it look like the matrix

set(h,'clim',[-1 1]); %<--- Makes the colors and values match

end

% the "a loop" means that the number of lines made of 1 or -1 is going to increase from 1 to 12,5%, 25%, 50%, 75% 87,5% and n-1 lines.

Also tried with "set(gca...", but didn't work, as it requires an specific object, I guess.

Any ideas?

Fangjun Jiang 2011-10-11

I am not sure what's wrong with your code. But when I run the following, it is exactly as expected. The top 2 rows are red, the bottom one row is gray.

cmap = [1,0,0;0.5,0.5,0.5;0,0,1]; % 1st row = red; 2nd = gray; 3rd = blue

%I have this matrix

A = [-1 -1 -1

-1 -1 -1

0 0 0];

a=A;a(end+1,:)=nan;a(:,end+1)=nan;

pcolor(a)

colormap(cmap);

axis ij; %<--- Flips the image to make it look like the matrix

caxis([-1 1]); %<--- Makes the colors and values match

Igor de Britto 2011-10-14

@Fangjun I managed to reinstall Matlab after getting a few more errors. Now the codes works just as expected!

@Fangjun, Elige and Teja: Can't really thank you enough! Things are looking pretty good now and you just made possible to make my masters graphics =). There are a few things to be done (like naming axis and the likes), but the crucial part was getting the plot collors right! Thanks a lot, people!

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