Re: No Show

*To*: mathgroup at smc.vnet.net*Subject*: [mg89112] Re: No Show*From*: Helen Read <hpr at together.net>*Date*: Mon, 26 May 2008 01:29:34 -0400 (EDT)*References*: <g1bf08$mcv$1@smc.vnet.net>*Reply-to*: HPR <read at math.uvm.edu>

Narasimham wrote: > 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] Oh, you are going to get a lot of replies to this. It was discussed at length when v.6 was first released. Basically, as of v.6, the default behavior of Show is to get the PlotRange from the first plot listed. See what happens if you reverse it. Show[bot, top] The way to get something more like you are expecting is to set PlotRange->Automatic within Show. 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 -> Automatic] You might also want to set the BoxRatios. 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 -> Automatic, BoxRatios -> {1, 1, 1}] I greatly dislike this new behavior of Show, for what it's worth. The folks at WRI argue that because of all the new graphics options (e.g., Filling), it would not make sense to combine the PlotRange automatically (as Show did in previous versions of Mathematica). Personally, I find it to be a pain in the neck to have to ask for PlotRange->Automatic virtually every time I use Show, and my students often forget and get burned by it. I would much prefer PlotRange->Automatic to be the default in Show, and to set my own PlotRange manually on those infrequent occasions when I need something else. And as for the argument that setting a PlotRange automatically from the combined plots isn't always appropriate, why not provide an easy way to tell Show to use the PlotRange from a particular plot? Something like PlotRange->{1} to get the PlotRange from the first plot, PlotRange->{2} to get the range from the 2nd plot, etc., would do the job when needed, and still allow PlotRange->Automatic (which for me is almost always what I want) to be the default. I just now discovered, BTW, that SetOptions[Show, PlotRange -> Automatic] does not even work. It generates an error message claiming that "PlotRange is not a known option for Show". -- Helen Read University of Vermont

**Follow-Ups**:**Re: No Show***From:*Narasimham <mathma18@hotmail.com>

**Re: Re: No Show***From:*Syd Geraghty <sydgeraghty@mac.com>

**Re: Re: No Show***From:*Andrzej Kozlowski <akoz@mimuw.edu.pl>