Compute the gamma function.
∞ / gamma (x) = |t^(x - 1) * exp (-t) dt / 0
Accuracy: The result is a valid enclosure. The result is tightest for X >= -10.
gamma (infsup (1.5)) ⇒ ans ⊂ [0.88622, 0.88623]
See also: @infsup/psi, @infsup/gammaln, @infsup/factorial.
Package: interval