the weight from MC and analytical calculation don't match
the MC within 1-st order diagram is consistent with direct integral;
a bug when using 0-order to renormalize.
integral inserted in self_consistent loop to compare Sigma, not succeed
yet
compare 0-order Sigma with Nikolay's
get the self-consistent loop with integration consistent with Nikolay's
Sigma_full.dat
find the right renormalizatin ratio for MC