!>
!> SLAORHR_COL_GETRFNP2 computes the modified LU factorization without
!> pivoting of a real general M-by-N matrix A. The factorization has
!> the form:
!>
!>     A - S = L * U,
!>
!> where:
!>    S is a m-by-n diagonal sign matrix with the diagonal D, so that
!>    D(i) = S(i,i), 1 <= i <= min(M,N). The diagonal D is constructed
!>    as D(i)=-SIGN(A(i,i)), where A(i,i) is the value after performing
!>    i-1 steps of Gaussian elimination. This means that the diagonal
!>    element at each step of  Gaussian elimination is at
!>    least one in absolute value (so that division-by-zero not
!>    possible during the division by the diagonal element);
!>
!>    L is a M-by-N lower triangular matrix with unit diagonal elements
!>    (lower trapezoidal if M > N);
!>
!>    and U is a M-by-N upper triangular matrix
!>    (upper trapezoidal if M < N).
!>
!> This routine is an auxiliary routine used in the Householder
!> reconstruction routine SORHR_COL. In SORHR_COL, this routine is
!> applied to an M-by-N matrix A with orthonormal columns, where each
!> element is bounded by one in absolute value. With the choice of
!> the matrix S above, one can show that the diagonal element at each
!> step of Gaussian elimination is the largest (in absolute value) in
!> the column on or below the diagonal, so that no pivoting is required
!> for numerical stability [1].
!>
!> For more details on the Householder reconstruction algorithm,
!> including the modified LU factorization, see [1].
!>
!> This is the recursive version of the LU factorization algorithm.
!> Denote A - S by B. The algorithm divides the matrix B into four
!> submatrices:
!>
!>        [  B11 | B12  ]  where B11 is n1 by n1,
!>    B = [ -----|----- ]        B21 is (m-n1) by n1,
!>        [  B21 | B22  ]        B12 is n1 by n2,
!>                               B22 is (m-n1) by n2,
!>                               with n1 = min(m,n)/2, n2 = n-n1.
!>
!>
!> The subroutine calls itself to factor B11, solves for B21,
!> solves for B12, updates B22, then calls itself to factor B22.
!>
!> For more details on the recursive LU algorithm, see [2].
!>
!> SLAORHR_COL_GETRFNP2 is called to factorize a block by the blocked
!> routine SLAORHR_COL_GETRFNP, which uses blocked code calling
!> Level 3 BLAS to update the submatrix. However, SLAORHR_COL_GETRFNP2
!> is self-sufficient and can be used without SLAORHR_COL_GETRFNP.
!>
!> [1] ,
!>     G. Ballard, J. Demmel, L. Grigori, M. Jacquelin, H.D. Nguyen,
!>     E. Solomonik, J. Parallel Distrib. Comput.,
!>     vol. 85, pp. 3-31, 2015.
!>
!> [2] , F. Gustavson, IBM J. of Res. and Dev.,
!>     vol. 41, no. 6, pp. 737-755, 1997.
!> 

M

!>          M is INTEGER
!>          The number of rows of the matrix A.  M >= 0.
!> 

N

!>          N is INTEGER
!>          The number of columns of the matrix A.  N >= 0.
!> 

A

!>          A is REAL array, dimension (LDA,N)
!>          On entry, the M-by-N matrix to be factored.
!>          On exit, the factors L and U from the factorization
!>          A-S=L*U; the unit diagonal elements of L are not stored.
!> 

LDA

!>          LDA is INTEGER
!>          The leading dimension of the array A.  LDA >= max(1,M).
!> 

D

!>          D is REAL array, dimension min(M,N)
!>          The diagonal elements of the diagonal M-by-N sign matrix S,
!>          D(i) = S(i,i), where 1 <= i <= min(M,N). The elements can
!>          be only plus or minus one.
!> 

INFO

!>          INFO is INTEGER
!>          = 0:  successful exit
!>          < 0:  if INFO = -i, the i-th argument had an illegal value
!> 

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!>
!> November 2019, Igor Kozachenko,
!>                Computer Science Division,
!>                University of California, Berkeley
!>
!>