add the ability to construct a qr factorization object via calling qr_factorize. This stores the qr factorization in householder form. Next, the product of a multiplication with Q can be constructed by using qmult. This prevents the explicit construction of Q, but allows one do also extract columns from Q by multiplication with unit vectors. Unlike the explicit factorization, if only a few columns of Q are needed, qr_factorize and qmult scale approximately quadratically instead of cubicly.
add the ability to construct a qr factorization object via calling qr_factorize. This stores the qr factorization in householder form. Next, the product of a multiplication with Q can be constructed by using qmult. This prevents the explicit construction of Q, but allows one do also extract columns from Q by multiplication with unit vectors. Unlike the explicit factorization, if only a few columns of Q are needed, qr_factorize and qmult scale approximately quadratically instead of cubicly.