# Using two color functions in a MatrixPlot

I'm trying to use two color functions within one MatrixPlot in Mathematica. Is it possible to do this?

For example, using a very simple matrix:

test = Partition[Table[i, {i, 1, 9}], 3]


I would like to make the even numbers vary in color increasing from white to red; and the odd numbers vary in color from grey to black.

How could I do this? I know how to get the whole matrix to vary in color, but no more than this.

I am not sure I understand. Here's what I understand:

You want to use MatrixPlot, the built-in command.

Then, the following might do what you want:

With[{max = Max@#},
MatrixPlot[#,
ColorFunction -> (If[EvenQ[#], Blend[{White, Red}, #/max],
Blend[{Gray, Black}, #/max]] &),
ColorFunctionScaling -> False]] &@test


Note that I use ColorFunctionScaling -> False, such that the even/odd numbers are still such (otherwise EvenQ doesn't make much sense. The max will be used for proper scaling. The output looks as follows:

• Thanks, that's exactly what I was looking for. Aug 19, 2013 at 15:02
• Is there any way to instead of saying is this an even number, use the coordinates of the square? For instance, in my real coding, I want to pick out the squares I indicated above, but they aren't all real numbers. So I wish to pick squares (1,2), (2,1), (2,3), (3,2) and scale them accordingly. Aug 19, 2013 at 15:05
• How do you mean, not real numbers? I am not sure I understand... we scale the 4 red sqaures according to the value there... Aug 19, 2013 at 16:01
• Sorry that didn't make sense. So instead, of just having a table of integers, I have a table of values that are solutions of an NDSolve. I want to colour the cells that I indicated by even numbers in this example. Once I don't have the odd and even distinction, my thinking was that it would be easier to pick out the coordinates (e.g. square (1,2), (2,1) etc...) Does that make any more sense? Aug 19, 2013 at 16:06
• I think I understand now. If you need that bit more flexibility, you might want to look at C.E.'s answer (you could stick to MatrixPlot I guess, using ColorRules or similar). Alternatively, you could use Graphic-primitives. As I still struggle to fully comprehend the problem, I am not sure how to adjust/edit Aug 19, 2013 at 16:34

For more flexibility, we can dump MatrixPlot and proceed with its core component, Raster:

max = 5;
test = RandomReal[max, {5, 5}];

colorfunc[val_, i_, max_] := If[EvenQ[i],
Blend[{White, Red}, val/max],
Blend[{Gray, Black}, val/max]
]
colormatrix[matrix_, max_] := Partition[
MapIndexed[colorfunc[#, First@#2, max] &, Flatten[matrix]],
Dimensions[matrix][[2]]
] /. {GrayLevel[a_] :> a {1, 1, 1}, RGBColor[b : _ ...] :> {b}};
Graphics[Raster[colormatrix[test, max]], Frame -> True]