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 >