# Hue function for negative arguments

I want to use Hue function for different colours with the argument being a function, i.e.,

Hue[f[i,j]]


Now, f[i,j] in my case can take negative values. The range of my function is [-2,2] (which can be rescaled to [-1,1] if necessary, by dividing the function by 2). The problem is that Hue automatically rescales its argument to put it into the range of [0,1). This is a problem for me as it will then show the same colour when my function is either -1 or 0 or 1, for example. The actual figure I want to work on can be generated by the following code:

Clear["Global*"];
n := 10;
angles = Table[RandomReal[{-Pi, Pi}], {i, n}, {j, n}];
f[here_, down_, right_] := Cos[down - here] + Cos[right - here]
g[list_, {i_, j_}] := Module[{m, n}, {m, n} = Dimensions[list]; {list[[i, j]],
If[i != m, list[[i + 1, j]], -list[[1, j]]],
If[j != n, list[[i, j + 1]], -list[[i, 1]]]}]
GraphicsGrid[ MapIndexed[ Graphics[{LightGray, Circle[{0, 0}, 1],
Hue[Rescale[f @@ g[angles, #2], {-2, 2}, {-1, 1}]], Thin,
Arrowheads[Small], Arrow[{{0, 0}, {Cos[#], Sin[#]}}]}] &, angles, {2}]]

• Why you dont you use Rescale like Rescale[..,{-2,2},{0,1}]? Hue will use the values of its first argument cyclically if they are outside the range $(0,1)$. – Spawn1701D Apr 25 '13 at 21:24
• To rephrase @Spawn's comment: Hue[] is a periodic function with period $1$, with the colors determined by the usual color wheel. Use Rescale[] if you want to use Hue[] for your desired range, with the caveat that due to the periodicity, Hue[0] and Hue[1] are both Red (RGBColor[1, 0, 0]). – J. M.'s technical difficulties Apr 26 '13 at 5:12

Hue does not rescale its argument, but it is a periodic function, equivalent to Hue[Mod[x, 1]]. What you need is rescaling: Rescale[f[...], {-2,2}]`.