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Mathematics Graphics and Visualization Wolfram Language

Plot3D with different colors for positive and negative values of z?

Cuneyt Eroglu

Posted 6 years ago

I am plotting a function z=f(x,y) using Plot3D. Plot3D[x^2 + y^2 - 100, {x, 1, 10}, {y, 1, 10}] How can I have different colors for positive and negative values of z? Many thanks in advance. Sincerely, Cuneyt

POSTED BY: Cuneyt Eroglu

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Cuneyt Eroglu

Posted 6 years ago

Much better! Thanks, Neil!

POSTED BY: Cuneyt Eroglu

Hans Dolhaine

Hans Dolhaine, retired

Posted 6 years ago

@ Neil: thanks a lot. I didn't know that, and I think it is not written very clearly in the "Help" ( Version 7.0 ). So I overlooked that. @Cuneyt Is this better? Plot3D[x^2 + y^2 - 100, {x, 1, 10}, {y, 1, 10}, ColorFunction -> Function[{x, y, z}, If[z > 0, Red, Blue]], ColorFunctionScaling -> False, PlotPoints -> 100]

POSTED BY: Hans Dolhaine

Neil Singer

Neil Singer, AC Kinetics, Inc.

Posted 6 years ago

Hans, You always need to use ColorFunctionScaling->False if you want to use absolute number values from the function. This works: Plot3D[x^2 + y^2 - 100, {x, 1, 10}, {y, 1, 10}, ColorFunction -> Function[{x, y, z}, If[z > 0, Hue[0.2], Hue[0.5]]], ColorFunctionScaling -> False] or Plot3D[x^2 + y^2 - 100, {x, 1, 10}, {y, 1, 10}, ColorFunction -> Function[{x, y, z}, If[z > 0, Red, Blue]], ColorFunctionScaling -> False] Regards, Neil

Hans,

You always need to use ColorFunctionScaling->False if you want to use absolute number values from the function.

This works:

Plot3D[x^2 + y^2 - 100, {x, 1, 10}, {y, 1, 10}, 
 ColorFunction -> Function[{x, y, z}, If[z > 0, Hue[0.2], Hue[0.5]]], 
 ColorFunctionScaling -> False]

Plot3D[x^2 + y^2 - 100, {x, 1, 10}, {y, 1, 10}, 
 ColorFunction -> Function[{x, y, z}, If[z > 0, Red, Blue]], 
 ColorFunctionScaling -> False]

Regards,

Neil

POSTED BY: Neil Singer

Cuneyt Eroglu

Posted 6 years ago

Hans and Neil, Thank you both for your responses. I have one more quick question. The boundary between the two colors is blurry. Is there a way to fix that? Sincerely, Cuneyt

POSTED BY: Cuneyt Eroglu

Hans Dolhaine

Hans Dolhaine, retired

Posted 6 years ago

Plot3D[x^2 + y^2 - 100, {x, 1, 10}, {y, 1, 10}, ColorFunction -> Function[{x, y, z}, Hue[z]]] But I have no idea why this doesn't work (at least on my system: Mma 7.0) Plot3D[x^2 + y^2 - 100, {x, 1, 10}, {y, 1, 10}, ColorFunction -> Function[{x, y, z}, If[z > 0, Hue[.02], Hue[.5]]]] Does somebody know?

Plot3D[x^2 + y^2 - 100, {x, 1, 10}, {y, 1, 10},  ColorFunction -> Function[{x, y, z}, Hue[z]]]

But I have no idea why this doesn't work (at least on my system: Mma 7.0)

Plot3D[x^2 + y^2 - 100, {x, 1, 10}, {y, 1, 10},  ColorFunction -> Function[{x, y, z}, If[z > 0, Hue[.02], Hue[.5]]]]

Does somebody know?

POSTED BY: Hans Dolhaine

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