Potential redundancy in computation of `ln_P_mu` function

[marmarmarmar]

I am curious whether this computation:

SpatialDE/Python-module/SpatialDE/aeh.py

Line 75 in 87b908b

ll = ll + np.linalg.det(K)

might be performed once and taken out of the loop. It does not seem to differ between different loop calls - so one may compute it once and save the computational time.