       Re: Plot3D with NDSolve

• To: mathgroup at smc.vnet.net
• Subject: [mg81686] Re: Plot3D with NDSolve
• From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
• Date: Mon, 1 Oct 2007 04:54:03 -0400 (EDT)
• Organization: The Open University, Milton Keynes, UK
• References: <fdnlg5\$klu\$1@smc.vnet.net>

```sean_incali wrote:
> Hello group,
>
> Let's say I can solve the following DE that depends on 2 paparmeters a
> and b, and plot it accordingly.
>
> eqn = y'[x] == b/(a y[x])
> par = {a -> 1, b -> 1}
>
> solution = NDSolve[{eqn /. par, y == 0.1}, y, {x, 0.1, 5}];
>
> Plot[y[x] /. solution, {x, 0.1, 5}];
>
> Above shows a 2d graph in x and y axes.
>
>
> What I want to do is now use one of the parameter as z axis.
>
> So I need to solve the DE while varying a from 1 to 5 for instance.
>
> Then I want to graph the solutions as a 3D object. with x. y and a
> axis (where a will be the new z axis.)
>
> I guess I can use Table to iterate the whole procedure, but I wanted
> to see how others would approach it.
>
> For instance, if I use
>
> eqn = y'[x] == b/(a y[x])
> par = {b -> 1}
>
> solution = Table[NDSolve[{eqn /. par, y == 0.1}, y, {x, 0.1, 5}],
> {a, 1, 5}];
>
> Plot[Evaluate[y[x] /. solution], {x, 0.1, 5}];
>
> It will shows all the solutions in one 2D graph. I want to see them in
> 3D.
>
> On the side note.. Why does the Plot require the "Evaluate" in the
> second code I posted and not in the first code???
>
> If someone can explain that that will be great also.
>
> Thanks in advance as usual.
>
> sean
>
>

Since it seems that you are using a version of Mathematica below 6.0, a
good way to achieve what you want is to use the *StackGraphics* as in

In:=
\$Version

Out=
5.2 for Microsoft Windows (June 20, 2005)

In:=
Needs["Graphics`Graphics3D`"]
eqn=y'[x]\[Equal]b/(a y[x]);
par={b\[Rule]1};

solution=Table[NDSolve[{eqn/.par,y\[Equal]0.1},y,{x,0.1,5}],{a,1,5}];

Block[{\$DisplayFunction=Identity},
gtab=Table[Plot[Evaluate[y[x]/.solution[[a]]],{x,0.1,5}],{a,1,5}];
]
Show[StackGraphics[gtab]];

HTH,
--
Jean-Marc

```

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