Find local differences in a matrix

This is an image palette containing RGB value

cmap=

0  0  0

0.5019  0  0

0.7529  0.7529  0.752

0  0.5019  0.5019

1  0  0

0.5019  0.5019  0.50196

0  0  0.50196

1  1  1

1  1  0

0.5019  0.5019  0

0  0  0

0  0  0

0  0  0

0  0  0

0  0  0

0  0  0

calculate this formula

D(cmap)=cmap(x,y)- cmap(x,y-1)

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After calculating D(cmap), Find

R=-(∑D(cmap))^2

Answer 1

[Andrei Bobrov]

D = diff(cmap,1,2);

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Answer 2

[David Sanchez]

For k=2:3
  D = cmap(:,k) - cmap(:,k-1);
end

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