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dgttrs

 NAME
      DGTTRS - solve one of the systems of equations  A*X = B or
      A'*X = B,

 SYNOPSIS
      SUBROUTINE DGTTRS( TRANS, N, NRHS, DL, D, DU, DU2, IPIV, B,
                         LDB, INFO )

          CHARACTER      TRANS

          INTEGER        INFO, LDB, N, NRHS

          INTEGER        IPIV( * )

          DOUBLE         PRECISION B( LDB, * ), D( * ), DL( * ),
                         DU( * ), DU2( * )

 PURPOSE
      DGTTRS solves one of the systems of equations
         A*X = B  or  A'*X = B, with a tridiagonal matrix A using
      the LU factorization computed by DGTTRF.

 ARGUMENTS
      TRANS   (input) CHARACTER
              Specifies the form of the system of equations:
              = 'N':  A * X = B  (No transpose)
              = 'T':  A'* X = B  (Transpose)
              = 'C':  A'* X = B  (Conjugate transpose = Transpose)

      N       (input) INTEGER
              The order of the matrix A.

      NRHS    (input) INTEGER
              The number of right hand sides, i.e., the number of
              columns of the matrix B.  NRHS >= 0.

      DL      (input) DOUBLE PRECISION array, dimension (N-1)
              The (n-1) multipliers that define the matrix L from
              the LU factorization of A.

      D       (input) DOUBLE PRECISION array, dimension (N)
              The n diagonal elements of the upper triangular
              matrix U from the LU factorization of A.

      DU      (input) DOUBLE PRECISION array, dimension (N-1)
              The (n-1) elements of the first superdiagonal of U.

      DU2     (input) DOUBLE PRECISION array, dimension (N-2)
              The (n-2) elements of the second superdiagonal of U.

      IPIV    (input) INTEGER array, dimension (N)

              The pivot indices; for 1 <= i <= n, row i of the
              matrix was interchanged with row IPIV(i).  IPIV(i)
              will always be either i or i+1; IPIV(i) = i indi-
              cates a row interchange was not required.

 (LDB,NRHS)
      B       (input/output) DOUBLE PRECISION array, dimension
              On entry, the right hand side matrix B.  On exit, B
              is overwritten by the solution matrix X.

      LDB     (input) INTEGER
              The leading dimension of the array B.  LDB >=
              max(1,N).

      INFO    (output) INTEGER
              = 0:  successful exit
              < 0:  if INFO = -i, the i-th argument had an illegal
              value