Evaluate the distance between two linear subspaces using the measure proposed by Li, Zha and Chiaromonte (2005).

`subspaceDistance(B0, B1)`

A single numeric value.

- B0
Matrix whose columns are a basis for the first subspace.

- B1
Matrix whose columns are a basis for the second subspace.

Matlab original by Yongtao Guan, translated to R by Suman Rakshit.

This algorithm calculates the maximum absolute value of the
eigenvalues of \(P1-P0\) where \(P0,P1\) are the projection
matrices onto the subspaces generated by `B0,B1`

.
This measure of distance was proposed by Li, Zha and Chiaromonte
(2005). See also Xia (2007).

Guan, Y. and Wang, H. (2010)
Sufficient dimension reduction for spatial point
processes directed by Gaussian random fields.
*Journal of the Royal Statistical Society, Series B*,
**72**, 367--387.

Li, B., Zha, H. and Chiaromonte, F. (2005) Contour regression: a
general approach to dimension reduction.
*Annals of Statistics* **33**, 1580--1616.

Xia, Y. (2007)
A constructive approach to the estimation of dimension reduction
directions.
*Annals of Statistics* **35**, 2654--2690.