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MathGroup Archive 2000

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integrity of ListContourPlot, ListDensityPlot

  • To: mathgroup at smc.vnet.net
  • Subject: [mg23730] integrity of ListContourPlot, ListDensityPlot
  • From: "Paul Hoke" <hokepaul at pilot.msu.edu>
  • Date: Mon, 5 Jun 2000 01:09:22 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

This question was raised after some help I received previously.

It appears that ListContourPlot and ListDensityPlot can sometimes in 
appropriately display colors if there are a few extreme points in the 
data field.

If the following notebook is run it works just fine:

"Needs <<Graphics`Legend`"
data = Table[
      10.*Sin[x + y]Cos[x - y], {x, xmin = -Pi, xmax = Pi, Pi/24.}, 
{y,
        ymin = -Pi, ymax = Pi, Pi/24.}];
Plot3D[10Sin[x + y]Cos[x - y], {x, xmin, xmax}, {y, ymin, ymax},
PlotPoints -> 25];
ShowLegend[
    ListContourPlot[data, ColorFunction -> (Hue[1 - #/2] &), Contours -> 
11,
      ContourLines -> False, DisplayFunction -> Identity], {Hue[1 - #/2] 
&,
      11, ToString[Min[data]], ToString[Max[data]],
      LegendPosition -> {1.1, -.4}}];
ShowLegend[
    ListDensityPlot[data, ColorFunction -> (Hue[1 - #/2] &), Mesh -> 
False,
      DisplayFunction -> Identity], {Hue[1 - #/2] &, 11, 
ToString[Max[data]],
      ToString[Min[data]], LegendPosition -> {1.1, -.4}}];



However, if the first data point is changed to -90 and then the entire 
re-plot the data, the all of the values appear to be represented 
incorrectly in the legend.  The minimum on the legend will be reported 
as -90 and all of the regions between -8 to -10 will appear as -60 when 
shaded if it is assumed that the legend applies a linear scale between 
the minimum and maximum
Insert the following into the above notebook (the matrixform is just to 
inspect the data to just to see the raw data table)
data[[1,1]]=-50
MatrixForm[data]

"Needs <<Graphics`Legend`"
data = Table[
      10.*Sin[x + y]Cos[x - y], {x, xmin = -Pi, xmax = Pi, Pi/24.}, 
{y,
        ymin = -Pi, ymax = Pi, Pi/24.}];
data[[1, 1]] = -90 ;
MatrixForm[data]
Plot3D[10Sin[x + y]Cos[x - y], {x, xmin, xmax}, {y, ymin, ymax},
PlotPoints -> 25];
ShowLegend[
    ListContourPlot[data, ColorFunction -> (Hue[1 - #/2] &), Contours -> 
11,
      ContourLines -> False, DisplayFunction -> Identity], {Hue[1 - #/2] 
&,
      11, ToString[Min[data]], ToString[Max[data]],
      LegendPosition -> {1.1, -.4}}];
ShowLegend[
    ListDensityPlot[data, ColorFunction -> (Hue[1 - #/2] &), Mesh -> 
False,
      DisplayFunction -> Identity], {Hue[1 - #/2] &, 11,
ToString[Max[data]],
      ToString[Min[data]], LegendPosition -> {1.1, -.4}}];


if anybody has any input regarding this phenomena, I would greatly 
appreciate it.

Thanks in advance,
Paul

________________________________
Paul Hoke
A107 Research Complex Engineering
Michigan State University
East Lansing MI 48824

Hokepaul at egr.msu.edu
Office 517.353.9952
Lab 517.353.6434
Fax 517.353.7179


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