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.])

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