Compute the QR decomposition of A.
A will be a subset of Q * R with orthogonal matrix Q and triangular matrix R.
The columns of Q are orthogonal unit vectors, that is, Q' * Q
equals the identity. R is an upper triangular matrix with positive
diagonal elements.
The result is returned in a permuted form, according to the optional return value P.
Accuracy: The result is a valid enclosure.
See also: @infsup/lu, @infsup/chol.
Package: interval