I have been studying symmetric indefinite matrices of fixed rank, which have been rather useful for a particular application. I wonder if there is a way to parameterise these by a smooth manifold, e.g., to do optimisation over them.
I have seen quite a few examples of similar structures, like the cone/manifold of positive semidefinite (PSD) matrices, the fixed rank manifold, the symmetric positive semidefinite fixed-ranked manifold, etc.
I am not so familiar with the literature; perhaps someone can share their knowledge on the possible geometry of symmetric indefinite matrices of fixed rank?