I am looking to rotate a 4th dimension array C[i,j,k,l] using a rotation matrix Q[i,j]. I already know how this is done in 3x3 matrices (Q.A.Transpose[Q]) but I am having a hard time doing it for a 3x3x3x3 matrix.
A mathematically correct expression would be
which is basically nested Sums, but I don't know how to code this in Mathematica.
