tensor rotation

I wish to rotate a tensor, T.

My understanding is that I can do so by creating a rotation matrix, R and then simply carry out the instruction:

Trot = R*T*R'

where Trot is the rotated tensor. I then use eig to determine the new Eigen vector directions. I find that sometimes I get results where the Eigen vectors are pointing in directions I do not expect.

However, when I use the same rotation matrix with the file transform.m from File Exchange

see here: http://www.mathworks.com/matlabcentral/fileexchange/8333-transform-tensor

then I find the tensor rotates nicely (albeit with some reversals of direction which I believe are due to the eig function).

I cannot figure out why the simple process of pre and post multiplying by the rotation matrix (and it's tranform) only works for some tensors and not others. I am not using the unit tensor (which does not rotate).

I would like to use the multiplication method so that I can vectorize what I am doing.

Any ideas?

Thanks Chris Walker