Is there any way to zero out a row or column of a DynamicSparseMatrix (depending on whether the matrix is stored in row or column major format)?
Presumably this should be a fairly efficient operation, since it just amounts to clearing the SparseVector for the given row.

Similarly, is there a way to erase an element from the matrix?

Indeed that does not seem to be easily doable at the moment. Probably because that's not common to want to suppress elements. If you are incrementally updating an assembled problem, perhaps it is better to start from a fresh matrix and copy what can be copied from the previous one... ??

btw, you are right in saying that would be very easy to implement. So feel free to add an entry in the bugtracker so that we don't forget about this feature (http://eigen.tuxfamily.org/bz/), and you could even propose a patch