Justin Chang <jychan...@gmail.com> writes: > Pardon me for my apparent lack of understanding over what may be simple > concepts, but why is div[u]*div[v] singular in the context of LSFEM?
The corresponding strong form is grad(div(u)). If u has n*d entries (in d dimensions -- it is a vector), div(u) has only n entries. That means grad(div(u)) must have a null space of dimension at least n*(d-1). If you a matrix A and a singular matrix B, then A + c*B cannot be well-conditioned for sufficiently large c.
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