SRC/sgetrf2.f(3)

NAME
SRC/sgetrf2.f

SYNOPSIS

  Functions/Subroutines
recursive subroutine sgetrf2 (m, n, a, lda, ipiv, info)
SGETRF2

Function/Subroutine Documentation

  recursive subroutine sgetrf2 (integer m, integer n, real, dimension( lda, * ) a, integer lda, integer, dimension( * ) ipiv, integer info)

SGETRF2

Purpose:

     SGETRF2 computes an LU factorization of a general M-by-N matrix A
     using partial pivoting with row interchanges.
     The factorization has the form
        A = P * L * U
     where P is a permutation matrix, L is lower triangular with unit
     diagonal elements (lower trapezoidal if m > n), and U is upper
     triangular (upper trapezoidal if m < n).
     This is the recursive version of the algorithm. It divides
     the matrix into four submatrices:
            [  A11 | A12  ]  where A11 is n1 by n1 and A22 is n2 by n2
        A = [ -----|----- ]  with n1 = min(m,n)/2
            [  A21 | A22  ]       n2 = n-n1
                                           [ A11 ]
     The subroutine calls itself to factor [ --- ],
                                           [ A12 ]
                     [ A12 ]
     do the swaps on [ --- ], solve A12, update A22,
                     [ A22 ]
     then calls itself to factor A22 and do the swaps on A21.

Parameters
    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 = P*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).

    IPIV

              IPIV is INTEGER array, dimension (min(M,N))
              The pivot indices; for 1 <= i <= min(M,N), row i of the
              matrix was interchanged with row IPIV(i).

    INFO

              INFO is INTEGER
              = 0:  successful exit
              < 0:  if INFO = -i, the i-th argument had an illegal value
              > 0:  if INFO = i, U(i,i) is exactly zero. The factorization
                    has been completed, but the factor U is exactly
                    singular, and division by zero will occur if it is used
                    to solve a system of equations.

Author
    Univ. of Tennessee

    Univ. of California Berkeley

    Univ. of Colorado Denver

    NAG Ltd.

Definition at line 112 of file sgetrf2.f.

Author

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