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Re: Problem with ColorFunction in ListDensityPlot in

  • To: mathgroup at smc.vnet.net
  • Subject: [mg102847] Re: [mg102839] Problem with ColorFunction in ListDensityPlot in
  • From: Patrick Scheibe <pscheibe at trm.uni-leipzig.de>
  • Date: Sun, 30 Aug 2009 06:06:39 -0400 (EDT)
  • References: <200908291030.GAA00291@smc.vnet.net>

Hi,

compare the following outputs

Reap@ListDensityPlot[
  Table[Sin[i + j^2], {i, 0, 3, 0.5}, {j, 0, 3, 0.5}], 
  ColorFunction -> ((Sow[{##}]; Hue[#]) &)];

and

Reap@ListPlot3D[Table[Sin[i + j^2], {i, 0, 3, 0.5}, {j, 0, 3, 0.5}], 
  ColorFunction -> ((Sow[{##}]; Hue[#]) &)]

you see, that the ListDensityPlot just doesn't get x,y and z values for
the ColorFunction. It only seems to receive the z values whereas the
ListPlot3D handles this differently. 

So you have to write

ListDensityPlot[Table[Sin[i + j^2], {i, 0, 3, 0.05}, {j, 0, 3, 0.05}],
  ColorFunction -> Function[{z}, Hue[z]]]

for Mathematica Version 7.
The strange thing is, that version 6 seems to handle this differently.
Compare in version 6 the output of 

Reap@ListDensityPlot[
  Table[Sin[i + j^2], {i, 0, 3, 0.5}, {j, 0, 3, 0.5}], 
  ColorFunction -> Function[{x, y, z}, Sow[{x, y, z}]; Hue[z]]]

and

Reap@ListDensityPlot[
  Table[Sin[i + j^2], {i, 0, 3, 0.5}, {j, 0, 3, 0.5}], 
  ColorFunction -> ((Sow[{##}]; Hue[#]) &)]

It seems that when they see a Function[{x,y,z},..] they give *all*
parameters and when they see a pure function they only give the
z-values. 

Can anyone resolve this?

Cheers
Patrick



On Sat, 2009-08-29 at 06:30 -0400, janey wrote:
> Has anyone tried using the ColorFunction option in ListDensityPlot? In
> version 6, the following works:
> 
> ListDensityPlot[Table[Sin[i+j^2],{i,0,3,0.05},{j,
> 0,3,0.05}],ColorFunction=EF=82=AEFunction[{x,y,z},Hue[z]]]
> 
> but not in version 7.
> 
> It only seems to work now with the preprogrammed defaults, or pure
> functions.
> 
> That example above is actually from the version 7 help page. It cannot
> even evaluate its own example
> 
> (see under  examples/scope/presentation, 2nd one down) which, f
> evaluated, results in an empty plot.
> Is this a bug? Is there a way around this that anybody knows of?
> 
> This problem exists in 7.0.0 and 7.1.0.
> 
> Thanks,
> Janey.
> 
> 



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