Introduce KhatriRaoMap
and FaceSplittingMap
#191
Merged
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This is a major improvement for a narrow, but potentially interesting case: MichielStock/Kronecker.jl#91.
EDIT: I realized it makes sense to introduce a
KhatriRaoMap
type, which corresponds to "columnwise Kronecker products". For not too small matricesA
andB
with equal number of columns (say larger than 5), map-vector-application is faster than what you get for a materialized matrix-vector product, besides the added benefit that this is lazy! In other languages, explicit versions seem to be pretty standard, see:https://docs.scipy.org/doc/scipy/reference/generated/scipy.linalg.khatri_rao.html
https://www.rdocumentation.org/packages/Matrix/versions/1.4-1/topics/KhatriRao
Unfortunately, I couldn't find an improved way to implement the rowwise Kronecker product, or "face-splitting product", but since it's related to the adjoint/transpose of the Khatri-Rao product, it's included anyway.