# how to define a gradient colormap

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ali eskandari on 4 Mar 2021
Edited: ali eskandari on 4 Mar 2021
I have different matrices with elements between zero and one, then I want to subtract some of them from each other and plot the output result on a gradient-scale colormap to see where the differences have happened.
I used imagesc to show the subtracted matrix, but the problem is that this function applies a map according to the range of the input matrix. For instance, in one case blue colour is mapped to -1, in another case blue might be map to another value. While I want to have a fix gradient map for values between -1 and 1. Is it possible to do that in Matlab?
For example, in plot one, the range of gradient is [-1,1], while on the others there is blue or red is assigned to different values. In fact, I want to see the effect of subtraction in different matrices while in the current colormap, I cannot understand whether there is any huge difference between them or not.

Jorg Woehl on 4 Mar 2021
Yes, you can use a fixed colormap by executing the following command each time you plot an image:
caxis([-1 1])
This will map all image points with values of -1 (or smaller) to the first row of the colormap (blue, in your case), and map all points with values of 1 (or higher) to the last row of the colormap (red).
Alternatively, you can call imagesc directly by supplying these color mapping limits:
imagesc(___, [-1 1])
Adam Danz on 4 Mar 2021
+1 Good idea to suggest the clim input, @Jorg Woehl

Adam Danz on 4 Mar 2021
Edited: Adam Danz on 4 Mar 2021
You need to define the colorscale using caxis.
caxis([-1,1])
to apply to all axes,
arrayfun(@(h)caxis(h,[.2,.6]),ax) % ax is an array of axis handles.

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