       Re: ContourPlot ColorFunction Question

• To: mathgroup at smc.vnet.net
• Subject: [mg119443] Re: ContourPlot ColorFunction Question
• From: Bob Hanlon <hanlonr at cox.net>
• Date: Sat, 4 Jun 2011 06:19:53 -0400 (EDT)

```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]

Bob Hanlon

---- Jody Sorensen <jodo11 at yahoo.com> 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: [mg119443] 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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