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Re: a question on ContourPlot

  • To: mathgroup at
  • Subject: [mg4533] Re: [mg4441] a question on ContourPlot
  • From: Allan Hayes <hay at>
  • Date: Wed, 7 Aug 1996 04:17:40 -0400
  • Sender: owner-wri-mathgroup at

"David E. Burmaster" <deb at>
>Subject: [mg4441] a question on ContourPlot
> I have made a complicated contour plot (on linear axes) that I
> would like to convert to semi-log axes....
> This does NOT work:
>	Show[ plot/.{a_, b_} -> {a, Log[b]}]
> That command converts the y-axis but does not transform the
> contours.....
> Could anyone pls suggest another approach?


	cp = ContourPlot[x^2 -y^2, {x,.001,2}, {y,.001,2.72}]
cp contains only a matrix of heights from which the polygons and  
lines are constructed. It also has the option
	MeshRange -> {{0.001, 2.}, {0.001, 2.72}}.
The only effect of
	cp/{a_, b_} -> {a, Log[b]}
on cp is to change this option to
	MeshRange -> {{0.001, 2.}, {-6.90776, 1.00063}}
which, in the display, merely changes the y-axis ticks, as you found.

However if you generate the contour lines and polygons (used for  
shading) explicitely
	gcp = Graphics[cp]
	lgcp = gcp/{a_?NumberQ, b_} -> {a, Log[b]}
will alter these elements as you want.
(You can see the internal form of cp... by using InputForm[cp] ...)
Allan Hayes
hay at



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