Performs an operation between a NxD array
 and a MxD array, returning a NxDxM array.
 Note if both inputs are NxD then the output
 will be NxDxN.

 Accepts: op  - matrix operation to perform (must be from core.matrix)
          xs  - NxD  array
          zs  - NxM  array
          bFlip - if true then NN is treated as
                  first input in op
Retuns: a NxDxM array

Performs an operation between a NxDxN array
 and a NxN array.

 Accepts: op  - matrix operation to perform (must be from core.matrix)
          NDN - NxDxN array
          NN  - NxN   array
          bFlip - if true then NN is treated as
                  first input in op
Retuns: a NxDxN array

Calls broadcast-function-NxD-MxD when given arrays and
just does standard broadcasting if one is a vector.
See broadcast-function-NxD-MxD for details on call
structure.

Sums out a dimension of nd-array.  Takes an array
 of matrix type and a dimension to sum out. Ensures
 no crash if X is nil.

Accepts: X - matrix
       dim - dimension to remove.

Returns: X with dim summed out

Scales the output from square-diff. Care should be taken
 to ensure inputs are of matrix type as will be slow
 otherwise.

 Accepts: x-sq-diff - NxDxM array to scale
          rho - vector of length scales

Returns: the scaled version of x-sq-diff

Calculates array of squared differences. Accepts an [N D] array of
points xs. Returns an [N D N] array in which entry [i d j] is given
by (xs[i,d] - xs[j,d])^2.