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dptsv

 NAME
      DPTSV - compute the solution to a real system of linear
      equations A*X = B, where A is an N-by-N symmetric positive
      definite tridiagonal matrix, and X and B are N-by-NRHS
      matrices

 SYNOPSIS
      SUBROUTINE DPTSV( N, NRHS, D, E, B, LDB, INFO )

          INTEGER       INFO, LDB, N, NRHS

          DOUBLE        PRECISION B( LDB, * ), D( * ), E( * )

 PURPOSE
      DPTSV computes the solution to a real system of linear equa-
      tions A*X = B, where A is an N-by-N symmetric positive
      definite tridiagonal matrix, and X and B are N-by-NRHS
      matrices.

      A is factored as A = L*D*L**T, and the factored form of A is
      then used to solve the system of equations.

 ARGUMENTS
      N       (input) INTEGER
              The order of the matrix A.  N >= 0.

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

      D       (input/output) DOUBLE PRECISION array, dimension (N)
              On entry, the n diagonal elements of the tridiagonal
              matrix A.  On exit, the n diagonal elements of the
              diagonal matrix D from the factorization A =
              L*D*L**T.

      E       (input/output) DOUBLE PRECISION array, dimension (N-
              1)
              On entry, the (n-1) subdiagonal elements of the tri-
              diagonal matrix A.  On exit, the (n-1) subdiagonal
              elements of the unit bidiagonal factor L from the
              L*D*L**T factorization of A.  (E can also be
              regarded as the superdiagonal of the unit bidiagonal
              factor U from the U**T*D*U factorization of A.)

      B       (input/output) DOUBLE PRECISION array, dimension (LDB,N)
              On entry, the N-by-NRHS right hand side matrix B.
              On exit, if INFO = 0, the N-by-NRHS 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
              > 0:  if INFO = i, the leading minor of order i is
              not positive definite, and the solution has not been
              computed.  The factorization has not been completed
              unless i = N.