Hi, I'm a new user of Eigen and I'm looking at using it for some QCD calculations. This involves having a 2x2 matrix where each entry is a 3x3 complex matrix. Each of these then sits in a bigger array - e.g. of size 16x16x16x48x4.( If it helps the 2x2 are quark spins, the 3x3 are QCD colour matrices and the rest are spacetime.)

I could just put the 2x2 part into my bigger array but would it be possible to to put the Scalar in the declaration as Matrix<complex<float>,3,3> so that I can perform usual linear algebra stuff on the 2x2 matrix. (I tried it naively but it didn't work and I couldn't find anything in the docs.) For example I need to take the product and trace of 2x2 matrices so that the 3x3 submatrices are multiplied and traced at the same time.

If I can do this, will it be faster than putting it in the array? I don't mind sacrificing a bit of speed in order to make the code easier to follow. Doing it component-wise would also be fine.

Thanks
Rachel