How to take log of sum product of matrix and e ^ x?

I wonder how to take the record of this sum function where it has $ e $ inside

$$ f (x) = sum_ {ij} (V_ {ij} e ^ {(x-N_ {ij}) ^ 2}) $$

where $ V_ {ij} $ Y $ N_ {ij} $ are the size of the matrix $ i times j $