"A block reflector is an orthogonal, symmetric matrix that reverses a subspace whose dimension may be greater than one."
- see abstract here http://locus.siam.org/SINUM/volume-25/art_0725014.html
It is built out of many elementary reflectors.
It is also referred to as a triangular factor, and is a triangular matrix and they are used in the Householder transformation.
A reflector belonging to can be written in the form : where is the identity matrix for, is a scalar and belongs to .
Read more about Block Reflector: LAPACK Routines
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