Re: Apparently easy ODE

• To: mathgroup at smc.vnet.net
• Subject: [mg22966] Re: Apparently easy ODE
• From: "Bill Bertram" <wkb at ansto.gov.au>
• Date: Fri, 7 Apr 2000 02:54:47 -0400 (EDT)
• Organization: Australian Nuclear Science and Technology Organisation
• References: <8chb0j\$9af@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```Kurt Taretto wrote in message <8chb0j\$9af at smc.vnet.net>...
>Hi, I'm having some problems solving PDE's, for example the folowing
>notebook
>
>
>Clear["Global`*"];
>
>(* constants definitions *)
>
>Es =11.8*8.85418`50*10^-14;
>q = 1.60218`50*10^-19;
>
>Nd = 1.0`50*^16; g = 1.0`50*^-4; G = 1.0`50*^20; u= 500.0`50; DD =
>25.0`50;
>k1 = q/Es;
>
>solution = NDSolve[{e'[x] == k1 p[x],
>
>        G - u e'[x] p[x] - u e[x] p'[x] + DD p''[x] == 0,
>
>        e'[0] == 0, p[g] == 1.0`50*^10, p'[0] == 0},
>
>      {e, p}, {x, 0, g}, WorkingPrecision -> 20];
>
>Plot[p[x] /. solution, {x, g/100, g}, PlotRange -> All];
>
>causes an error message, "Cannot find starting value for the variable
>x.", and obviously no solution is given.  Apparently this error message
>is about the internals of the algorithm, but I can't figure out what I'm
>doing wrong.  Any help on this would be appreciated.

Hi Kurt

Yours is a boundary value problem for which Mathematica V4 can only handle a
single DE.

Cheers,

Bill

```

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