       Infinite expression, NDSolve

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• Subject: [mg128401] Infinite expression, NDSolve
• From: Grasley <grasley at gmail.com>
• Date: Tue, 16 Oct 2012 03:22:16 -0400 (EDT)
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```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!

```

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