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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( * )



     #include <sunperf.h>

     void dptsv(int n, int nrhs, double  *d,  double  *e,  double
               *db, int ldb, int *info) ;

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 tridiago-
               nal 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
               tridiagonal matrix A.  On exit, the (n-1) subdiag-
               onal 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 factoriza-
               tion 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 ille-
               gal 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.

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