I have a `3xN` array, conceptually an array of `N` 3-vectors, I want to construct the 
array which results from matrix multiplying a given `3x3` matrix with each column of the 
array. Is there a good way to do this in a vectorized manner?

Currently, my problem is `3xN`, but I may need to consider `3xNxM` (or more) in the future.

Loopy approach

```
U=numpy.rand( [3,24] )

R=numpy.eye(3) # placeholder

for i in xrange( U.shape[1]):
    U[:,i]=numpy.dot( R, U[:,i] )

```