[petsc-users] floating region help

[Jed Brown]

2011/9/20 Gong Ding <gdiso at ustc.edu>

> Since the conductance of left part and right part is low, the middle region
> is floating.
>

Not really floating, just sensitive to parameters. It has a unique value, of
physical interest, but if you change the conductivity or thickness of the
thin region on either side, then it's value changes significantly. This is
an ill-conditioned problem, but it's ill-conditioned for physically
meaningful reasons. It's not singular and the smallest singular value has
great significance, so a null space method is not appropriate. You could
reformulate for a slightly different problem which would have a constant
null space, but not for this problem.
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