Infinite expression, NDSolve

*To*: mathgroup at smc.vnet.net*Subject*: [mg128401] Infinite expression, NDSolve*From*: Grasley <grasley at gmail.com>*Date*: Tue, 16 Oct 2012 03:22:16 -0400 (EDT)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*Delivered-to*: l-mathgroup@wolfram.com*Delivered-to*: mathgroup-newout@smc.vnet.net*Delivered-to*: mathgroup-newsend@smc.vnet.net

Dear All, I am trying to use NDSolve to solve the heat equation for 1-D radial flow in cylindrical coordinates, with the initial condition of a spatially constant temperature, and boundary conditions of zero flux at r=0 (axisymmetry) and a constant temperature at a radius of 1. Here is the code: NDSolve[{D[T[r, t], t] == 1/r*D[r D[T[r, t], r], r], Derivative[1, 0][T][0, t] == 0, T[1, t] == 20, T[r, 0] == 0}, T, {r, 0, 1}, {t, 0, 10}] Power::infy: Infinite expression 1/0. encountered. >> Infinity::indet: Indeterminate expression 0. ComplexInfinity encountered. >> Power::infy: Infinite expression 1/0. encountered. >> Infinity::indet: Indeterminate expression 0. ComplexInfinity encountered. >> NDSolve::ndnum: Encountered non-numerical value for a derivative at t == 0.`. >> I've tried using nonzero (i.e. very small values) for the initial time and in place of r=0 in the boundary condition, but to no avail. Any ideas? Thanks!