Angle between two subspaces.
SUBSPACE(A,B) finds the angle between two subspaces specified
by the columns of A and B. If A and B are vectors of unit
length, this is the same as ACOS (A'*B).
If the angle is small, the two spaces are nearly linearly
dependent. In a physical experiment described by some
observations A, and a second realization of the experiment
described by B, SUBSPACE(A,B) gives a measure of the amount
of new information afforded by the second experiment not
associated with statistical errors of fluctuations.