Re: Problem with partial differential equations

*To*: mathgroup at smc.vnet.net*Subject*: [mg23465] Re: Problem with partial differential equations*From*: Max Ulbrich <mulbrich at physik.tu-muenchen.de>*Date*: Thu, 11 May 2000 00:54:14 -0400 (EDT)*Organization*: Rechenzentrum der Max-Planck-Gesellschaft in Garching*References*: <8etp9i$n1n@smc.vnet.net> <BH0R4.93$5j.5351@ralph.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Hi Roland, I tried, but I still get an error message like NDSolve::ndnum: The right-hand side of the differential equation does not evaluate to a number at t == 0. Has anyone an idea what is wrong? Max Roland Franzius wrote: > Hi Max, > seems to work if you use delayed definitions (at evalutation time) > > > P1[x_,t_]:=2x^2; > > P2[x_,t_]:=2(x+t)^2; > > Diff=0.2; > > G[x_]:=Exp[-x^2]; > > probably a problem of fixing variables to numbers > > Max Ulbrich wrote: > > > > Hi, > > > > I have a problem with a partial differential equation. > > I want to solve a diffusion problem in a time-dependent potential. > > It works with the potential P1, but not with P2. > > Can someone help me? > > > > P1[x_,t_]=2x^2; > > P2[x_,t_]=2(x+t)^2; > > Diff=0.2; > > G[x_]=Exp[-x^2]; > > solution=n/.First[ > > NDSolve[{Derivative[0,1][n][x,t]== > > > > Diff*Derivative[2,0][n][x,t]+n[x,t]*Derivative[2,0][P1][x,t]+ > > > > Derivative[1,0][n][x,t]*Derivative[1,0][P1][x,t],n[x,0]==G[x], > > n[-3,t]==G[-3],n[3,t]==G[3]},n,{x,-3,3},{t,0,4}, > > StartingStepSize->0.05]]; > > Plot3D[solution[x,t],{x,-2,2},{t,0,4}]; > > > > Max Ulbrich > > ulbrich at biochem.mpg.de > > -- > Roland Franzius > > +++ exactly <<n>> lines of this message have value <<FALSE>> +++