# How do I make a red and blue colormap?

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L'O.G. on 15 Sep 2022
Commented: Star Strider on 15 Sep 2022
I can plot a matrix of integers using imagesc. How do I make a discrete colormap (i.e., only for the integers) with a gradient of red colors for positive values and a gradient of blue colors for negative values, with zero being white? Also, the numbers aren't symmetric about zero, i.e., they range from [-2,5] so I want a deep blue for -2 and a deep red for 5. I hope that makes sense.
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### Accepted Answer

Star Strider on 15 Sep 2022
I am not exactly certain what you want, however the basic colormap is easy to create —
cm = [1 0 0; 1 1 1; 0 0 1]; % Basic Colormap
cmi = interp1([-2; 0; 5], cm, (-2:5)) % interpolated Colormap
cmi = 8×3
1.0000 0 0 1.0000 0.5000 0.5000 1.0000 1.0000 1.0000 0.8000 0.8000 1.0000 0.6000 0.6000 1.0000 0.4000 0.4000 1.0000 0.2000 0.2000 1.0000 0 0 1.0000
M = randi([-2 5],9) % Matrix
M = 9×9
-1 5 3 -2 -1 -2 3 2 3 1 1 -2 1 0 4 -2 1 -2 2 0 5 -1 4 -1 2 -2 0 0 2 0 -1 5 -1 -2 4 1 -2 1 1 3 -2 4 -1 -1 1 2 1 4 4 0 1 5 1 3 5 0 4 1 4 3 -2 4 -2 -2 4 -2 1 1 3 4 1 -2 5 4 5 4 -2 3 2 -2 0
figure
imagesc(M)
colormap(cmi)
Experiment to get different results.
.
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Star Strider on 15 Sep 2022
As always, my pleasure!

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