# 1/r terms in {cylindrical, spherical} coordinates

Asked by
Nico Schlömer

I'm solving several PDEs in cylindrical coordinates, where there terms 1/r typically occurs, e.g.,

d/dr( 1/r d(r*U)/dr ) + .... = rhs.

This appears to be a problem at first when the domain includes r=0, but really isn't when Dirichlet boundary conditions are chosen at r=0. Then, all trial functions for u increase linearly in r-direction (or vanish around r=0) and the finite element formulation

1/r d(r*u)/dr * dv/dr = (u + 1/r du/dr) * dv/dr

is indeed bounded.

Do I have to take any particular care when throwing this thing at Dolfin? How are the boundary conditions applied?

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