Method on @infsup: ei (X)

Compute the exponential integral for positive arguments.

          x
         /  exp (t)
ei (x) = |--------- dt
         /     t
       -∞

Accuracy: The result is a tight enclosure.

ei (infsup (1))
  ⇒ ans ⊂ [1.8951, 1.8952]

Package: interval