Re: No Show

• To: mathgroup at smc.vnet.net
• Subject: [mg89167] Re: No Show
• From: Narasimham <mathma18 at hotmail.com>
• Date: Wed, 28 May 2008 04:43:39 -0400 (EDT)
• References: <g1bf08\$mcv\$1@smc.vnet.net> <g1di00\$9np\$1@smc.vnet.net>

```On May 25, 10:31 pm, Helen Read <h... at together.net> wrote:
> 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".
>
> --
> University of Vermont

Plot command should be "stand alone", should not depend on Plot
History.Pity if captured data is discarded due to command history.
Plot3D should be a stand alone instruction.Once a user is conditioned /
accustomed/pampered  in a certain way the previlige should perhaps not
be withdrawn without sufficient reason.That is a suggestion anyway...

Thanks for all these responses.

Narasimham

```

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