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Re: No Show

  • To: mathgroup at smc.vnet.net
  • Subject: [mg89122] Re: No Show
  • From: "David Park" <djmpark at comcast.net>
  • Date: Mon, 26 May 2008 01:31:24 -0400 (EDT)
  • References: <g1bf08$mcv$1@smc.vnet.net>

It's because of the strange way that Show picks up plot options. It's 
picking up the PlotRange (and I also think the actual BoxRatios) from the 
first top Plot3D. So you can solve the problem by supplying the correct 
option values in the Show statement.

bot = Plot3D[-Sqrt[1 - (x^2 + y^2)], {x, -1, 1}, {y, -1, 1}];
top = Plot3D[+Sqrt[1 - (x^2 + y^2)], {x, -1, 1}, {y, -1, 1}];

Show[top, bot,
 PlotRange -> {-1, 1},
 BoxRatios -> 1]

Or, in this case, you could actually combine the two surfaces in one Plot3D 
statement.

Plot3D[{-Sqrt[1 - (x^2 + y^2)], Sqrt[1 - (x^2 + y^2)]}, {x, -1, 1}, {y, -1, 
1}, BoxRatios -> 1]

With the Presentations package there is a cleaner separation between options 
that affect the drawing of the graphical objects and the options that 
control the overall appearance of the plot. The problem does not occur there 
so the following works as expected.

Needs["Presentations`Master`"]

Draw3DItems[
 {Draw3D[-Sqrt[1 - (x^2 + y^2)], {x, -1, 1}, {y, -1, 1}],
  Draw3D[Sqrt[1 - (x^2 + y^2)], {x, -1, 1}, {y, -1, 1}]},
 Axes -> True]

Also, PlotRange is an option that affects both the drawing of a graphical 
object AND the overall appearance of a plot. Sometimes it has to appear in 
both places. For example, if you are combining a 2D contour plot with other 
elements you may need a z-range in the contour plot, but certainly not in 
the overall plot.

-- 
David Park
djmpark at comcast.net
http://home.comcast.net/~djmpark/


"Narasimham" <mathma18 at hotmail.com> wrote in message 
news:g1bf08$mcv$1 at smc.vnet.net...
> Why is the following plot, bot, (with - Sqrt) not Shown along with
> top?
>
> Why is it treated only as a plot skeleton, so no combining is
> possible?
>
> bot = Plot3D[-Sqrt[1 - (x^2 + y^2) ] , {x, -1, 1}, {y, -1, 1}]
> top = Plot3D[+Sqrt[1 - (x^2 + y^2) ] , {x, -1, 1}, {y, -1, 1}]
> Show[top, bot]
>
> TIA
> Narasimham
> 



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