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