MATLAB find() / Numpy nonzero idioms for Eigen

Question

Chances are this is a very stupid question but I spent a pretty absurd amount of time looking for it on the documentation, to no avail.

in MATLAB, the find() function gi

Answer 1

This might work for you and others who check this out. In order to set elements of a matrix m based on the condition on another matrix A, you can use this notation:

m = (A.array() != 0).select(1, m);

This command replaces those elements in matrix m that have non-zero corresponding elements in A, with one.