Concatenation of Kronecker Products

[MKAbdElrahman]

I'm taking Kronecker products of sparse matrices. when I concatenate these matrices, full dense matrices are returned which is very unefficient.

[dkarrasch]

As in #76, I recommend doing "higher-order" manipulations like linear combinations and concatenation of Kronecker products with LinearMaps.jl. You are not restricted to use its own Kronecker product, but can safely use the types of Kronecker.jl.

[MKAbdElrahman]

This works, but doesn't mesh well with the iterativesolvers package. The performance is so slow even for small matrices.
I used the kron function from LinearMaps.jl and performance is good.

[MichielStock]

Strange, can you give a small working example?