Annotation of rpl/lapack/lapack/dgetrs.f, revision 1.1
1.1 ! bertrand 1: SUBROUTINE DGETRS( TRANS, N, NRHS, A, LDA, IPIV, B, LDB, 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: CHARACTER TRANS
! 10: INTEGER INFO, LDA, LDB, N, NRHS
! 11: * ..
! 12: * .. Array Arguments ..
! 13: INTEGER IPIV( * )
! 14: DOUBLE PRECISION A( LDA, * ), B( LDB, * )
! 15: * ..
! 16: *
! 17: * Purpose
! 18: * =======
! 19: *
! 20: * DGETRS solves a system of linear equations
! 21: * A * X = B or A' * X = B
! 22: * with a general N-by-N matrix A using the LU factorization computed
! 23: * by DGETRF.
! 24: *
! 25: * Arguments
! 26: * =========
! 27: *
! 28: * TRANS (input) CHARACTER*1
! 29: * Specifies the form of the system of equations:
! 30: * = 'N': A * X = B (No transpose)
! 31: * = 'T': A'* X = B (Transpose)
! 32: * = 'C': A'* X = B (Conjugate transpose = Transpose)
! 33: *
! 34: * N (input) INTEGER
! 35: * The order of the matrix A. N >= 0.
! 36: *
! 37: * NRHS (input) INTEGER
! 38: * The number of right hand sides, i.e., the number of columns
! 39: * of the matrix B. NRHS >= 0.
! 40: *
! 41: * A (input) DOUBLE PRECISION array, dimension (LDA,N)
! 42: * The factors L and U from the factorization A = P*L*U
! 43: * as computed by DGETRF.
! 44: *
! 45: * LDA (input) INTEGER
! 46: * The leading dimension of the array A. LDA >= max(1,N).
! 47: *
! 48: * IPIV (input) INTEGER array, dimension (N)
! 49: * The pivot indices from DGETRF; for 1<=i<=N, row i of the
! 50: * matrix was interchanged with row IPIV(i).
! 51: *
! 52: * B (input/output) DOUBLE PRECISION array, dimension (LDB,NRHS)
! 53: * On entry, the right hand side matrix B.
! 54: * On exit, the solution matrix X.
! 55: *
! 56: * LDB (input) INTEGER
! 57: * The leading dimension of the array B. LDB >= max(1,N).
! 58: *
! 59: * INFO (output) INTEGER
! 60: * = 0: successful exit
! 61: * < 0: if INFO = -i, the i-th argument had an illegal value
! 62: *
! 63: * =====================================================================
! 64: *
! 65: * .. Parameters ..
! 66: DOUBLE PRECISION ONE
! 67: PARAMETER ( ONE = 1.0D+0 )
! 68: * ..
! 69: * .. Local Scalars ..
! 70: LOGICAL NOTRAN
! 71: * ..
! 72: * .. External Functions ..
! 73: LOGICAL LSAME
! 74: EXTERNAL LSAME
! 75: * ..
! 76: * .. External Subroutines ..
! 77: EXTERNAL DLASWP, DTRSM, XERBLA
! 78: * ..
! 79: * .. Intrinsic Functions ..
! 80: INTRINSIC MAX
! 81: * ..
! 82: * .. Executable Statements ..
! 83: *
! 84: * Test the input parameters.
! 85: *
! 86: INFO = 0
! 87: NOTRAN = LSAME( TRANS, 'N' )
! 88: IF( .NOT.NOTRAN .AND. .NOT.LSAME( TRANS, 'T' ) .AND. .NOT.
! 89: $ LSAME( TRANS, 'C' ) ) THEN
! 90: INFO = -1
! 91: ELSE IF( N.LT.0 ) THEN
! 92: INFO = -2
! 93: ELSE IF( NRHS.LT.0 ) THEN
! 94: INFO = -3
! 95: ELSE IF( LDA.LT.MAX( 1, N ) ) THEN
! 96: INFO = -5
! 97: ELSE IF( LDB.LT.MAX( 1, N ) ) THEN
! 98: INFO = -8
! 99: END IF
! 100: IF( INFO.NE.0 ) THEN
! 101: CALL XERBLA( 'DGETRS', -INFO )
! 102: RETURN
! 103: END IF
! 104: *
! 105: * Quick return if possible
! 106: *
! 107: IF( N.EQ.0 .OR. NRHS.EQ.0 )
! 108: $ RETURN
! 109: *
! 110: IF( NOTRAN ) THEN
! 111: *
! 112: * Solve A * X = B.
! 113: *
! 114: * Apply row interchanges to the right hand sides.
! 115: *
! 116: CALL DLASWP( NRHS, B, LDB, 1, N, IPIV, 1 )
! 117: *
! 118: * Solve L*X = B, overwriting B with X.
! 119: *
! 120: CALL DTRSM( 'Left', 'Lower', 'No transpose', 'Unit', N, NRHS,
! 121: $ ONE, A, LDA, B, LDB )
! 122: *
! 123: * Solve U*X = B, overwriting B with X.
! 124: *
! 125: CALL DTRSM( 'Left', 'Upper', 'No transpose', 'Non-unit', N,
! 126: $ NRHS, ONE, A, LDA, B, LDB )
! 127: ELSE
! 128: *
! 129: * Solve A' * X = B.
! 130: *
! 131: * Solve U'*X = B, overwriting B with X.
! 132: *
! 133: CALL DTRSM( 'Left', 'Upper', 'Transpose', 'Non-unit', N, NRHS,
! 134: $ ONE, A, LDA, B, LDB )
! 135: *
! 136: * Solve L'*X = B, overwriting B with X.
! 137: *
! 138: CALL DTRSM( 'Left', 'Lower', 'Transpose', 'Unit', N, NRHS, ONE,
! 139: $ A, LDA, B, LDB )
! 140: *
! 141: * Apply row interchanges to the solution vectors.
! 142: *
! 143: CALL DLASWP( NRHS, B, LDB, 1, N, IPIV, -1 )
! 144: END IF
! 145: *
! 146: RETURN
! 147: *
! 148: * End of DGETRS
! 149: *
! 150: END
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