Doing SparseMat (sparse matrix) operations in openCV

Question

I need to do matrix operations (mainly multiply and inverse) of a sparse matrix SparseMat in OpenCV.
I noticed that you can only iterate and insert values to SparseMat.
Is there an external code I can use? (or am I missing something?)

Answer 1

It's just that sparse matrices are not really suited for inversion or matrix-matrix-multiplication, so it's quite reasonable there is no builtin function for that. They're actually more used for matrix-vector multiplication (usually when solving iterative linear systems).

What you can do is solve N linear systems (with the columns of the identity matrix as right hand sides) to get the inverse matrix. But then you need N*N storage for the inverse matrix anyway, so using a dense matrix with a usual decompositions algorithm would be a better way to do it, as the performance gain won't be that high when doing N iterative solutions. Or maybe some sparse direct solvers like SuperLU or TAUCS may help, but I doubt that OpenCV has such functionalities.

You should also think if you really need the inverse matrix. Often such problem are also solvable by just solving a linear system, which can be done with a sparse matrix quite easily and fast via e.g. CG or BiCGStab.