DGTTRS(3)      LAPACK routine of NEC Numeric Library Collection      DGTTRS(3)



NAME
       DGTTRS

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



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




ARGUMENTS
           TRANS     (input)
                     TRANS is CHARACTER*1
                     Specifies the form of the system of equations.
                     = 'N':  A * X = B  (No transpose)
                     = 'T':  A**T* X = B  (Transpose)
                     = 'C':  A**T* X = B  (Conjugate transpose = Transpose)

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

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

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

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

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

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

           IPIV      (input)
                     IPIV is 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 indicates a row interchange was not
                     required.

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

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

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



LAPACK routine                  31 October 2017                      DGTTRS(3)