   LDB &gt;= MAX(1,M), if LTRANS = .FALSE.,
          LDB &gt;= MAX(1,N), if LTRANS = .TRUE..

  TAU     (output) DOUBLE PRECISION array of dimension (MIN(N,M))
          This array contains the scalar factors of the elementary
          reflectors defining the matrix P.

  U       (output) DOUBLE PRECISION array of dimension (LDU,N)
          The leading N-by-N upper triangular part of this array
          contains the Cholesky factor of the solution matrix X of
          the problem, X = op(U)'*op(U).
   