This is a wrapper for general dense or sparse dot products.
It is not necessary except as a common interface for supporting ndarray, scipy spmatrix, and PySparse arrays.
Returns a dense (1 x n) vector with unbiased estimators for the column variances for each column of the (m x n) sparse or dense matrix A. (The normalization is by (m - 1).)
>>> a = numpy.array([[1,2], [3,4]], 'd') >>> columnvariances(a) array([ 2., 2.])