gammainc, no small outputs

[Anderson M. Winkler]

Dear all,

Consider this:

Matlab: 

>> gammainc(60,6,'upper')

ans =

   6.1802e-20

Octave 4.0.0 (same for 3.8.2):

>> gammainc(60,6,'upper')

ans = 0

This is causing large problems, as norminv(6.1802e-20) = -9.0659 (the expected result), whereas norminv(0) = -Inf, and subsequent code crashes.

Could this be fixed to allow outputs smaller than about 1e-16? Thanks.

All the best,

Anderson