Annotation of rpl/lapack/lapack/dgetrf.f, revision 1.1
1.1 ! bertrand 1: SUBROUTINE DGETRF( 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: * DGETRF 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 3 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 = -i, the i-th argument had an illegal value
! 54: * > 0: if INFO = i, U(i,i) 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
! 63: PARAMETER ( ONE = 1.0D+0 )
! 64: * ..
! 65: * .. Local Scalars ..
! 66: INTEGER I, IINFO, J, JB, NB
! 67: * ..
! 68: * .. External Subroutines ..
! 69: EXTERNAL DGEMM, DGETF2, DLASWP, DTRSM, XERBLA
! 70: * ..
! 71: * .. External Functions ..
! 72: INTEGER ILAENV
! 73: EXTERNAL ILAENV
! 74: * ..
! 75: * .. Intrinsic Functions ..
! 76: INTRINSIC MAX, MIN
! 77: * ..
! 78: * .. Executable Statements ..
! 79: *
! 80: * Test the input parameters.
! 81: *
! 82: INFO = 0
! 83: IF( M.LT.0 ) THEN
! 84: INFO = -1
! 85: ELSE IF( N.LT.0 ) THEN
! 86: INFO = -2
! 87: ELSE IF( LDA.LT.MAX( 1, M ) ) THEN
! 88: INFO = -4
! 89: END IF
! 90: IF( INFO.NE.0 ) THEN
! 91: CALL XERBLA( 'DGETRF', -INFO )
! 92: RETURN
! 93: END IF
! 94: *
! 95: * Quick return if possible
! 96: *
! 97: IF( M.EQ.0 .OR. N.EQ.0 )
! 98: $ RETURN
! 99: *
! 100: * Determine the block size for this environment.
! 101: *
! 102: NB = ILAENV( 1, 'DGETRF', ' ', M, N, -1, -1 )
! 103: IF( NB.LE.1 .OR. NB.GE.MIN( M, N ) ) THEN
! 104: *
! 105: * Use unblocked code.
! 106: *
! 107: CALL DGETF2( M, N, A, LDA, IPIV, INFO )
! 108: ELSE
! 109: *
! 110: * Use blocked code.
! 111: *
! 112: DO 20 J = 1, MIN( M, N ), NB
! 113: JB = MIN( MIN( M, N )-J+1, NB )
! 114: *
! 115: * Factor diagonal and subdiagonal blocks and test for exact
! 116: * singularity.
! 117: *
! 118: CALL DGETF2( M-J+1, JB, A( J, J ), LDA, IPIV( J ), IINFO )
! 119: *
! 120: * Adjust INFO and the pivot indices.
! 121: *
! 122: IF( INFO.EQ.0 .AND. IINFO.GT.0 )
! 123: $ INFO = IINFO + J - 1
! 124: DO 10 I = J, MIN( M, J+JB-1 )
! 125: IPIV( I ) = J - 1 + IPIV( I )
! 126: 10 CONTINUE
! 127: *
! 128: * Apply interchanges to columns 1:J-1.
! 129: *
! 130: CALL DLASWP( J-1, A, LDA, J, J+JB-1, IPIV, 1 )
! 131: *
! 132: IF( J+JB.LE.N ) THEN
! 133: *
! 134: * Apply interchanges to columns J+JB:N.
! 135: *
! 136: CALL DLASWP( N-J-JB+1, A( 1, J+JB ), LDA, J, J+JB-1,
! 137: $ IPIV, 1 )
! 138: *
! 139: * Compute block row of U.
! 140: *
! 141: CALL DTRSM( 'Left', 'Lower', 'No transpose', 'Unit', JB,
! 142: $ N-J-JB+1, ONE, A( J, J ), LDA, A( J, J+JB ),
! 143: $ LDA )
! 144: IF( J+JB.LE.M ) THEN
! 145: *
! 146: * Update trailing submatrix.
! 147: *
! 148: CALL DGEMM( 'No transpose', 'No transpose', M-J-JB+1,
! 149: $ N-J-JB+1, JB, -ONE, A( J+JB, J ), LDA,
! 150: $ A( J, J+JB ), LDA, ONE, A( J+JB, J+JB ),
! 151: $ LDA )
! 152: END IF
! 153: END IF
! 154: 20 CONTINUE
! 155: END IF
! 156: RETURN
! 157: *
! 158: * End of DGETRF
! 159: *
! 160: END
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