Re: trouble solving partial DE

*To*: mathgroup at smc.vnet.net*Subject*: [mg39923] Re: trouble solving partial DE*From*: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>*Date*: Wed, 12 Mar 2003 02:28:07 -0500 (EST)*Organization*: Universitaet Leipzig*References*: <b4k48f$8ip$1@smc.vnet.net>*Reply-to*: kuska at informatik.uni-leipzig.de*Sender*: owner-wri-mathgroup at wolfram.com

Hi, for what is the first argument in u[x,t] ?? You have only derivatives with respect to t and it is an ordinary differential equation for u[t]. But you gave not an intial condition u[x,0]==0 *and* Derivative[0,1][u][x,0]==blubBlub you gave D[u[L, 0], t] == 0 and this evaluates to True, and Mathematica miss a second initial condition. Regards Jens karlo jolic wrote: > > Hi everyone > > I keeping getting the following error: > > NDSolve::"deql": "The first argument must have both an equation and an \ > > initial condition." > > when i try to solve the following second order partial differential > equation > (wherein the function u is a function of variables x and t): > > NDSolve[{m*D[u[x, t], t, t] + 6*Pi*n*r*D[u[x, t], t] - > 0.5*mu*i*ndash*pm*((L - u[x, t])^2/(R^2 + (L - u[x, t])^2)^1.5 > - > 1/(R^2 + (L - u[x, t])^2)^0.5 - (L + u[x, t])^2/(R^2 + (L + > u[x, t])^2)^1.5 + > 1/(R^2 + (L + u[x, t])^2)^0.5) == 0, > u[L, 0] == L, > D[u[L, 0], t] == 0}, > u, {x, 0, L}, {t, 0, 1}] > > I have specified 2 initial conditions already, so i can't understand why > i get the error. > > does anyone know whats the problem? > > Thanks > > Karlo > PS I'm relatively new at mathematica.