Annotation of rpl/lapack/lapack/dgetf2.f, revision 1.1
1.1 ! bertrand 1: SUBROUTINE DGETF2( M, N, A, LDA, IPIV, INFO )
! 2: *
! 3: * -- LAPACK routine (version 3.2) --
! 4: * -- LAPACK is a software package provided by Univ. of Tennessee, --
! 5: * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
! 6: * November 2006
! 7: *
! 8: * .. Scalar Arguments ..
! 9: INTEGER INFO, LDA, M, N
! 10: * ..
! 11: * .. Array Arguments ..
! 12: INTEGER IPIV( * )
! 13: DOUBLE PRECISION A( LDA, * )
! 14: * ..
! 15: *
! 16: * Purpose
! 17: * =======
! 18: *
! 19: * DGETF2 computes an LU factorization of a general m-by-n matrix A
! 20: * using partial pivoting with row interchanges.
! 21: *
! 22: * The factorization has the form
! 23: * A = P * L * U
! 24: * where P is a permutation matrix, L is lower triangular with unit
! 25: * diagonal elements (lower trapezoidal if m > n), and U is upper
! 26: * triangular (upper trapezoidal if m < n).
! 27: *
! 28: * This is the right-looking Level 2 BLAS version of the algorithm.
! 29: *
! 30: * Arguments
! 31: * =========
! 32: *
! 33: * M (input) INTEGER
! 34: * The number of rows of the matrix A. M >= 0.
! 35: *
! 36: * N (input) INTEGER
! 37: * The number of columns of the matrix A. N >= 0.
! 38: *
! 39: * A (input/output) DOUBLE PRECISION array, dimension (LDA,N)
! 40: * On entry, the m by n matrix to be factored.
! 41: * On exit, the factors L and U from the factorization
! 42: * A = P*L*U; the unit diagonal elements of L are not stored.
! 43: *
! 44: * LDA (input) INTEGER
! 45: * The leading dimension of the array A. LDA >= max(1,M).
! 46: *
! 47: * IPIV (output) INTEGER array, dimension (min(M,N))
! 48: * The pivot indices; for 1 <= i <= min(M,N), row i of the
! 49: * matrix was interchanged with row IPIV(i).
! 50: *
! 51: * INFO (output) INTEGER
! 52: * = 0: successful exit
! 53: * < 0: if INFO = -k, the k-th argument had an illegal value
! 54: * > 0: if INFO = k, U(k,k) is exactly zero. The factorization
! 55: * has been completed, but the factor U is exactly
! 56: * singular, and division by zero will occur if it is used
! 57: * to solve a system of equations.
! 58: *
! 59: * =====================================================================
! 60: *
! 61: * .. Parameters ..
! 62: DOUBLE PRECISION ONE, ZERO
! 63: PARAMETER ( ONE = 1.0D+0, ZERO = 0.0D+0 )
! 64: * ..
! 65: * .. Local Scalars ..
! 66: DOUBLE PRECISION SFMIN
! 67: INTEGER I, J, JP
! 68: * ..
! 69: * .. External Functions ..
! 70: DOUBLE PRECISION DLAMCH
! 71: INTEGER IDAMAX
! 72: EXTERNAL DLAMCH, IDAMAX
! 73: * ..
! 74: * .. External Subroutines ..
! 75: EXTERNAL DGER, DSCAL, DSWAP, XERBLA
! 76: * ..
! 77: * .. Intrinsic Functions ..
! 78: INTRINSIC MAX, MIN
! 79: * ..
! 80: * .. Executable Statements ..
! 81: *
! 82: * Test the input parameters.
! 83: *
! 84: INFO = 0
! 85: IF( M.LT.0 ) THEN
! 86: INFO = -1
! 87: ELSE IF( N.LT.0 ) THEN
! 88: INFO = -2
! 89: ELSE IF( LDA.LT.MAX( 1, M ) ) THEN
! 90: INFO = -4
! 91: END IF
! 92: IF( INFO.NE.0 ) THEN
! 93: CALL XERBLA( 'DGETF2', -INFO )
! 94: RETURN
! 95: END IF
! 96: *
! 97: * Quick return if possible
! 98: *
! 99: IF( M.EQ.0 .OR. N.EQ.0 )
! 100: $ RETURN
! 101: *
! 102: * Compute machine safe minimum
! 103: *
! 104: SFMIN = DLAMCH('S')
! 105: *
! 106: DO 10 J = 1, MIN( M, N )
! 107: *
! 108: * Find pivot and test for singularity.
! 109: *
! 110: JP = J - 1 + IDAMAX( M-J+1, A( J, J ), 1 )
! 111: IPIV( J ) = JP
! 112: IF( A( JP, J ).NE.ZERO ) THEN
! 113: *
! 114: * Apply the interchange to columns 1:N.
! 115: *
! 116: IF( JP.NE.J )
! 117: $ CALL DSWAP( N, A( J, 1 ), LDA, A( JP, 1 ), LDA )
! 118: *
! 119: * Compute elements J+1:M of J-th column.
! 120: *
! 121: IF( J.LT.M ) THEN
! 122: IF( ABS(A( J, J )) .GE. SFMIN ) THEN
! 123: CALL DSCAL( M-J, ONE / A( J, J ), A( J+1, J ), 1 )
! 124: ELSE
! 125: DO 20 I = 1, M-J
! 126: A( J+I, J ) = A( J+I, J ) / A( J, J )
! 127: 20 CONTINUE
! 128: END IF
! 129: END IF
! 130: *
! 131: ELSE IF( INFO.EQ.0 ) THEN
! 132: *
! 133: INFO = J
! 134: END IF
! 135: *
! 136: IF( J.LT.MIN( M, N ) ) THEN
! 137: *
! 138: * Update trailing submatrix.
! 139: *
! 140: CALL DGER( M-J, N-J, -ONE, A( J+1, J ), 1, A( J, J+1 ), LDA,
! 141: $ A( J+1, J+1 ), LDA )
! 142: END IF
! 143: 10 CONTINUE
! 144: RETURN
! 145: *
! 146: * End of DGETF2
! 147: *
! 148: END
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