Return to dtrtrs.f CVS log

Up to [local] / rpl / lapack / lapack

Annotation of rpl/lapack/lapack/dtrtrs.f, revision 1.1

1.1     ! bertrand    1:       SUBROUTINE DTRTRS( UPLO, TRANS, DIAG, N, NRHS, A, LDA, B, LDB,
        !             2:      $                   INFO )
        !             3: *
        !             4: *  -- LAPACK routine (version 3.2) --
        !             5: *  -- LAPACK is a software package provided by Univ. of Tennessee,    --
        !             6: *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
        !             7: *     November 2006
        !             8: *
        !             9: *     .. Scalar Arguments ..
        !            10:       CHARACTER          DIAG, TRANS, UPLO
        !            11:       INTEGER            INFO, LDA, LDB, N, NRHS
        !            12: *     ..
        !            13: *     .. Array Arguments ..
        !            14:       DOUBLE PRECISION   A( LDA, * ), B( LDB, * )
        !            15: *     ..
        !            16: *
        !            17: *  Purpose
        !            18: *  =======
        !            19: *
        !            20: *  DTRTRS solves a triangular system of the form
        !            21: *
        !            22: *     A * X = B  or  A**T * X = B,
        !            23: *
        !            24: *  where A is a triangular matrix of order N, and B is an N-by-NRHS
        !            25: *  matrix.  A check is made to verify that A is nonsingular.
        !            26: *
        !            27: *  Arguments
        !            28: *  =========
        !            29: *
        !            30: *  UPLO    (input) CHARACTER*1
        !            31: *          = 'U':  A is upper triangular;
        !            32: *          = 'L':  A is lower triangular.
        !            33: *
        !            34: *  TRANS   (input) CHARACTER*1
        !            35: *          Specifies the form of the system of equations:
        !            36: *          = 'N':  A * X = B  (No transpose)
        !            37: *          = 'T':  A**T * X = B  (Transpose)
        !            38: *          = 'C':  A**H * X = B  (Conjugate transpose = Transpose)
        !            39: *
        !            40: *  DIAG    (input) CHARACTER*1
        !            41: *          = 'N':  A is non-unit triangular;
        !            42: *          = 'U':  A is unit triangular.
        !            43: *
        !            44: *  N       (input) INTEGER
        !            45: *          The order of the matrix A.  N >= 0.
        !            46: *
        !            47: *  NRHS    (input) INTEGER
        !            48: *          The number of right hand sides, i.e., the number of columns
        !            49: *          of the matrix B.  NRHS >= 0.
        !            50: *
        !            51: *  A       (input) DOUBLE PRECISION array, dimension (LDA,N)
        !            52: *          The triangular matrix A.  If UPLO = 'U', the leading N-by-N
        !            53: *          upper triangular part of the array A contains the upper
        !            54: *          triangular matrix, and the strictly lower triangular part of
        !            55: *          A is not referenced.  If UPLO = 'L', the leading N-by-N lower
        !            56: *          triangular part of the array A contains the lower triangular
        !            57: *          matrix, and the strictly upper triangular part of A is not
        !            58: *          referenced.  If DIAG = 'U', the diagonal elements of A are
        !            59: *          also not referenced and are assumed to be 1.
        !            60: *
        !            61: *  LDA     (input) INTEGER
        !            62: *          The leading dimension of the array A.  LDA >= max(1,N).
        !            63: *
        !            64: *  B       (input/output) DOUBLE PRECISION array, dimension (LDB,NRHS)
        !            65: *          On entry, the right hand side matrix B.
        !            66: *          On exit, if INFO = 0, the solution matrix X.
        !            67: *
        !            68: *  LDB     (input) INTEGER
        !            69: *          The leading dimension of the array B.  LDB >= max(1,N).
        !            70: *
        !            71: *  INFO    (output) INTEGER
        !            72: *          = 0:  successful exit
        !            73: *          < 0: if INFO = -i, the i-th argument had an illegal value
        !            74: *          > 0: if INFO = i, the i-th diagonal element of A is zero,
        !            75: *               indicating that the matrix is singular and the solutions
        !            76: *               X have not been computed.
        !            77: *
        !            78: *  =====================================================================
        !            79: *
        !            80: *     .. Parameters ..
        !            81:       DOUBLE PRECISION   ZERO, ONE
        !            82:       PARAMETER          ( ZERO = 0.0D+0, ONE = 1.0D+0 )
        !            83: *     ..
        !            84: *     .. Local Scalars ..
        !            85:       LOGICAL            NOUNIT
        !            86: *     ..
        !            87: *     .. External Functions ..
        !            88:       LOGICAL            LSAME
        !            89:       EXTERNAL           LSAME
        !            90: *     ..
        !            91: *     .. External Subroutines ..
        !            92:       EXTERNAL           DTRSM, XERBLA
        !            93: *     ..
        !            94: *     .. Intrinsic Functions ..
        !            95:       INTRINSIC          MAX
        !            96: *     ..
        !            97: *     .. Executable Statements ..
        !            98: *
        !            99: *     Test the input parameters.
        !           100: *
        !           101:       INFO = 0
        !           102:       NOUNIT = LSAME( DIAG, 'N' )
        !           103:       IF( .NOT.LSAME( UPLO, 'U' ) .AND. .NOT.LSAME( UPLO, 'L' ) ) THEN
        !           104:          INFO = -1
        !           105:       ELSE IF( .NOT.LSAME( TRANS, 'N' ) .AND. .NOT.
        !           106:      $         LSAME( TRANS, 'T' ) .AND. .NOT.LSAME( TRANS, 'C' ) ) THEN
        !           107:          INFO = -2
        !           108:       ELSE IF( .NOT.NOUNIT .AND. .NOT.LSAME( DIAG, 'U' ) ) THEN
        !           109:          INFO = -3
        !           110:       ELSE IF( N.LT.0 ) THEN
        !           111:          INFO = -4
        !           112:       ELSE IF( NRHS.LT.0 ) THEN
        !           113:          INFO = -5
        !           114:       ELSE IF( LDA.LT.MAX( 1, N ) ) THEN
        !           115:          INFO = -7
        !           116:       ELSE IF( LDB.LT.MAX( 1, N ) ) THEN
        !           117:          INFO = -9
        !           118:       END IF
        !           119:       IF( INFO.NE.0 ) THEN
        !           120:          CALL XERBLA( 'DTRTRS', -INFO )
        !           121:          RETURN
        !           122:       END IF
        !           123: *
        !           124: *     Quick return if possible
        !           125: *
        !           126:       IF( N.EQ.0 )
        !           127:      $   RETURN
        !           128: *
        !           129: *     Check for singularity.
        !           130: *
        !           131:       IF( NOUNIT ) THEN
        !           132:          DO 10 INFO = 1, N
        !           133:             IF( A( INFO, INFO ).EQ.ZERO )
        !           134:      $         RETURN
        !           135:    10    CONTINUE
        !           136:       END IF
        !           137:       INFO = 0
        !           138: *
        !           139: *     Solve A * x = b  or  A' * x = b.
        !           140: *
        !           141:       CALL DTRSM( 'Left', UPLO, TRANS, DIAG, N, NRHS, ONE, A, LDA, B,
        !           142:      $            LDB )
        !           143: *
        !           144:       RETURN
        !           145: *
        !           146: *     End of DTRTRS
        !           147: *
        !           148:       END