Re: ContourPlot ColorFunction Question

• To: mathgroup at smc.vnet.net
• Subject: [mg119457] Re: ContourPlot ColorFunction Question
• From: Heike Gramberg <heike.gramberg at gmail.com>
• Date: Sun, 5 Jun 2011 07:01:26 -0400 (EDT)

```You need to specify ColorFunctionScaling -> False to prevent the coordinates from being rescaled:

Plot[x /. Solve[x^2 + c == x, x], {c, -2, 2}, Frame -> True,
Axes -> False, PlotRange -> {-2, 2}, AspectRatio -> 1,
ColorFunction -> (If[#2 > 0, Red, Green] &),
ColorFunctionScaling -> False]

Heike

On 4 Jun 2011, at 11:21, Jody Sorensen wrote:

> Thanks for the suggestions.  It's an improvement, but it still doesn't do what I think it should be doing.  In this simple example:
>
> Plot[x /. Solve[x^2 + c == x, x], {c, -3, 2}, Frame -> True,
> Axes -> False, PlotRange -> {-2, 2}, AspectRatio -> 1,
> ColorFunction -> (If[#2 > 0, Red, Green] &)]
>
> the whole graph is drawn in red, whereas anything below the axis should be green.
>
> Any ideas?
>
> Jody Sorensen
>
> --- On Fri, 6/3/11, Bob Hanlon <hanlonr at cox.net> wrote:
>
> From: Bob Hanlon <hanlonr at cox.net>
> Subject: [mg119452] Re: [mg119436] ContourPlot ColorFunction Question
> To: mathgroup at smc.vnet.net, "Jody Sorensen" <jodo11 at yahoo.com>
> Date: Friday, June 3, 2011, 7:26 AM
>
>
> For ContourPlot, there is only one argument for ColorFunction. That argument is the contour levels.
>
> ContourPlot[x^2 + c - x, {c, -2, 2}, {x, -2, 2},
> ColorFunction -> (If[# > 0, Red, Green] &),
> Contours -> {0}]
>
> Plot[
> Evaluate[x /. Solve[x^2 + c == x, x]],
> {c, -2, 2},
> Frame -> True,
> Axes -> False,
> PlotRange -> {-2, 2},
> AspectRatio -> 1,
> PlotStyle -> {Green, Red}]
>
> Plot[
> x /. Solve[x^2 + c == x, x],
> {c, -2, 2},
> Frame -> True,
> Axes -> False,
> PlotRange -> {-2, 2},
> AspectRatio -> 1,
> ColorFunction -> (If[2 #2 > 1, Red, Green] &)]
>
>
> Bob Hanlon
>
> ---- Jody Sorensen <jodo11 at yahoo.com> wrote:
>
> ====================================================
> I'm new to this list and possibly out of my depth, but I'd appreciate any help on this issue.
>
> We are trying to plot an implicit function using ContourPlot and have the points on the curve colored based on the x and y values (which we call c and x) - specifically based on the value of the derivative.
>
> We have tried things like the following without success, even though similar commands work with Plot:
> ContourPlot[x^2+c = x, {c, -2, 2}, {x, -2, 2},
> ColorFunction -> (If[2 #1 > 1, Red, Green] &)]
>
> Any suggestions or solutions would be great to hear!
>
> Thanks!
> Jody Sorensen

```

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