def _ln_choose(n, k_agg):
gammaln = special.gammaln<EOL>return gammaln(n + <NUM_LIT:1>) - (gammaln(k_agg + <NUM_LIT:1>) + gammaln(n - k_agg + <NUM_LIT:1>))<EOL>
log binomial coefficient with extended gamma factorials. n and k_agg may be
int or array - if both array, must be the same length.