Return to dgttrs.f CVS log

Up to [local] / rpl / lapack / lapack

Mise à jour globale de Lapack 3.2.2.

    1:       SUBROUTINE DGTTRS( TRANS, N, NRHS, DL, D, DU, DU2, IPIV, 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          TRANS
   11:       INTEGER            INFO, LDB, N, NRHS
   12: *     ..
   13: *     .. Array Arguments ..
   14:       INTEGER            IPIV( * )
   15:       DOUBLE PRECISION   B( LDB, * ), D( * ), DL( * ), DU( * ), DU2( * )
   16: *     ..
   17: *
   18: *  Purpose
   19: *  =======
   20: *
   21: *  DGTTRS solves one of the systems of equations
   22: *     A*X = B  or  A'*X = B,
   23: *  with a tridiagonal matrix A using the LU factorization computed
   24: *  by DGTTRF.
   25: *
   26: *  Arguments
   27: *  =========
   28: *
   29: *  TRANS   (input) CHARACTER*1
   30: *          Specifies the form of the system of equations.
   31: *          = 'N':  A * X = B  (No transpose)
   32: *          = 'T':  A'* X = B  (Transpose)
   33: *          = 'C':  A'* X = B  (Conjugate transpose = Transpose)
   34: *
   35: *  N       (input) INTEGER
   36: *          The order of the matrix A.
   37: *
   38: *  NRHS    (input) INTEGER
   39: *          The number of right hand sides, i.e., the number of columns
   40: *          of the matrix B.  NRHS >= 0.
   41: *
   42: *  DL      (input) DOUBLE PRECISION array, dimension (N-1)
   43: *          The (n-1) multipliers that define the matrix L from the
   44: *          LU factorization of A.
   45: *
   46: *  D       (input) DOUBLE PRECISION array, dimension (N)
   47: *          The n diagonal elements of the upper triangular matrix U from
   48: *          the LU factorization of A.
   49: *
   50: *  DU      (input) DOUBLE PRECISION array, dimension (N-1)
   51: *          The (n-1) elements of the first super-diagonal of U.
   52: *
   53: *  DU2     (input) DOUBLE PRECISION array, dimension (N-2)
   54: *          The (n-2) elements of the second super-diagonal of U.
   55: *
   56: *  IPIV    (input) INTEGER array, dimension (N)
   57: *          The pivot indices; for 1 <= i <= n, row i of the matrix was
   58: *          interchanged with row IPIV(i).  IPIV(i) will always be either
   59: *          i or i+1; IPIV(i) = i indicates a row interchange was not
   60: *          required.
   61: *
   62: *  B       (input/output) DOUBLE PRECISION array, dimension (LDB,NRHS)
   63: *          On entry, the matrix of right hand side vectors B.
   64: *          On exit, B is overwritten by the solution vectors X.
   65: *
   66: *  LDB     (input) INTEGER
   67: *          The leading dimension of the array B.  LDB >= max(1,N).
   68: *
   69: *  INFO    (output) INTEGER
   70: *          = 0:  successful exit
   71: *          < 0:  if INFO = -i, the i-th argument had an illegal value
   72: *
   73: *  =====================================================================
   74: *
   75: *     .. Local Scalars ..
   76:       LOGICAL            NOTRAN
   77:       INTEGER            ITRANS, J, JB, NB
   78: *     ..
   79: *     .. External Functions ..
   80:       INTEGER            ILAENV
   81:       EXTERNAL           ILAENV
   82: *     ..
   83: *     .. External Subroutines ..
   84:       EXTERNAL           DGTTS2, XERBLA
   85: *     ..
   86: *     .. Intrinsic Functions ..
   87:       INTRINSIC          MAX, MIN
   88: *     ..
   89: *     .. Executable Statements ..
   90: *
   91:       INFO = 0
   92:       NOTRAN = ( TRANS.EQ.'N' .OR. TRANS.EQ.'n' )
   93:       IF( .NOT.NOTRAN .AND. .NOT.( TRANS.EQ.'T' .OR. TRANS.EQ.
   94:      $    't' ) .AND. .NOT.( TRANS.EQ.'C' .OR. TRANS.EQ.'c' ) ) THEN
   95:          INFO = -1
   96:       ELSE IF( N.LT.0 ) THEN
   97:          INFO = -2
   98:       ELSE IF( NRHS.LT.0 ) THEN
   99:          INFO = -3
  100:       ELSE IF( LDB.LT.MAX( N, 1 ) ) THEN
  101:          INFO = -10
  102:       END IF
  103:       IF( INFO.NE.0 ) THEN
  104:          CALL XERBLA( 'DGTTRS', -INFO )
  105:          RETURN
  106:       END IF
  107: *
  108: *     Quick return if possible
  109: *
  110:       IF( N.EQ.0 .OR. NRHS.EQ.0 )
  111:      $   RETURN
  112: *
  113: *     Decode TRANS
  114: *
  115:       IF( NOTRAN ) THEN
  116:          ITRANS = 0
  117:       ELSE
  118:          ITRANS = 1
  119:       END IF
  120: *
  121: *     Determine the number of right-hand sides to solve at a time.
  122: *
  123:       IF( NRHS.EQ.1 ) THEN
  124:          NB = 1
  125:       ELSE
  126:          NB = MAX( 1, ILAENV( 1, 'DGTTRS', TRANS, N, NRHS, -1, -1 ) )
  127:       END IF
  128: *
  129:       IF( NB.GE.NRHS ) THEN
  130:          CALL DGTTS2( ITRANS, N, NRHS, DL, D, DU, DU2, IPIV, B, LDB )
  131:       ELSE
  132:          DO 10 J = 1, NRHS, NB
  133:             JB = MIN( NRHS-J+1, NB )
  134:             CALL DGTTS2( ITRANS, N, JB, DL, D, DU, DU2, IPIV, B( 1, J ),
  135:      $                   LDB )
  136:    10    CONTINUE
  137:       END IF
  138: *
  139: *     End of DGTTRS
  140: *
  141:       END