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How to create personalized colormap that starts from a specified value

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Reza Lashani
Reza Lashani 2022-11-22
评论： Reza Lashani 2022-11-22
Hello everyone
I've plotted a surface which it's value when z>=0 is what I want to report. When I use zlim([0 n]) command, the colormap won't update and the peaks are not distinguishable as you see in pictures attached. Is there a way that I could create a personalized colormap which it starts from z=0 and vary with z value? (For example in the grey gradient in pictures attached, the color of z=0 becomes black and the color of highest value of z becomes grey)
Thanks and regards

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Florian Bidaud
Florian Bidaud 2022-11-22
Ran in:
Hi
If Z is the map you plot, you can replace all the negative values by 0 like that :
Z = [0 1 8; -1 5 10;-6 -3 14]
Z = 3×3
0 1 8 -1 5 10 -6 -3 14
Z_negative = Z;
Z_negative(Z<0) = 0
Z_negative = 3×3
0 1 8 0 5 10 0 0 14
And then plot this new map
If you don't want these values at all, you can replace them by NaN :
Z = [0 1 8; -1 5 10;-6 -3 14];
Z_negative = Z;
Z_negative(Z<0) = NaN
Z_negative = 3×3
0 1 8 NaN 5 10 NaN NaN 14
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Florian Bidaud
Florian Bidaud 2022-11-22
编辑：Florian Bidaud 2022-11-22
I'm not sure what you really want. zlim removes the values from the plot as follows:
Maybe what you want is changing the color scale ? In this case, you need to use caxis([0 n]).
x = [0 1 2 3 4];
y = [0 1 2 3 4];
z = [1 5 -2 4 6;-1 5 -6 7 8; 1 2 5 9 10; -2 -3 -4 -5 -7;5 -1 6 -2 3];
surf(x,y,z)
zlim([0 max(max(z))])
caxis([0 max(max(z))])

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