In Eigen 3.2.9 the follow code is fast/instantaneous:
Eigen::SparseMatrix<double> I = Eigen::SparseMatrix<double>(100000,100000);
Eigen::SparseMatrix<double> B = I / 100.0;
this suggests that Eigen was only doing the division on the non-zeros (and there aren't any so it's fast).
However, in Eigen 3.3.1 and 3.3.90 the code takes _a very long time_ and uses >1GB in memory. This suggests that its using dense rather than sparse math.
In my library we're doing operations like this to sparse matrices all of the time. Is this sparse matrix divided by scalar no longer supported?
Thank you for the report.
Summary: Bug 1384: fix evaluation of "sparse/scalar" that used the wrong evaluation path.