Compute the real n-th root of X.
Accuracy: The result is a valid enclosure. The result is a tight enclosure for n ≥ -2. The result also is a tight enclosure if the reciprocal of n can be computed exactly in double-precision.
See also: @infsup/pown, @infsup/pownrev, @infsup/realsqrt, @infsup/cbrt.
Package: interval