       Re:Coloring 2DPlot with different colors

• To: mathgroup at yoda.physics.unc.edu
• Subject: Re:Coloring 2DPlot with different colors
• From: "Dr A. Hayes" <hay at leicester.ac.uk>
• Date: Sat, 11 Jun 1994 13:29:06 +0100 (BST)

```Jian-hua writes:
> Does any one knows how to make on 2DPlot with different colors? For
> example, I'd like to use two different color to emphasize decreasing or
> increasing of a function or the positive and negative values of a > function.

The basic idea is to get at the Line object in the  -Graphics- output and
change it in the way that you want..
You can see this code by using InputForm.
I have left the code pretty rough in the interests of explicitness.
You could also colour according to slope.

(Plot[Sin[x],{x,0,2Pi}, DisplayFunction->Identity]
/.Line[p_]
:> Line/@Partition[p,2,1]
/.ln:Line[{{x1_,y1_},{x2_,y2_}}]
:> {If[y1<=y2, Hue,Hue[2/3]],ln}
);
Show[%, DisplayFunction->\$DisplayFunction]

(Plot[Sin[x],{x,0,2Pi}, DisplayFunction->Identity]
/.Line[p_]
:> Line/@Partition[p,2,1]
/.Line[{{x1_,y1_},{x2_,y2_}}]/;y1 y2 <0
:> {Line[{{x1,y1},{x2,0}}], Line[{{x1,0},{x2,y2}}]}
/.ln:Line[{{x1_,y1_},{x2_,y2_}}]
:> {If[Max[y1,y2] <=0,Hue,Hue[2/3]],ln}
);
Show[%, DisplayFunction->\$DisplayFunction]

Allan Hayes,
hay at le.ac.uk

```

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