Created attachment 585 [details]
compile and run
We run a large simulation program, which makes use of the sparse capabilities of Eigen. One unexpected simulation scenario lead to the case that we tried to invert a Matrix part, which did not include any components different to zero. It took us a while to figure out, that out program got stuck at the attempt to factorize a zero matrix. Of course there is no sense in factorizing a Zero-Matrix.
If there is no factorization possible, is there any hint given from eigen to detect this? In the actual implementation, the factorize method just never returns, although it should be easy to detect the zero matrix.
The attachment gives a minimal example of this behavior.