```
```

### 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 N, NRHS, LDB, INFO
DOUBLE PRECISION D(*), E(*), B(LDB,*)

SUBROUTINE DPTSV_64(N, NRHS, D, E, B, LDB, INFO)

INTEGER*8 N, NRHS, LDB, INFO
DOUBLE PRECISION D(*), E(*), B(LDB,*)

F95 INTERFACE
SUBROUTINE PTSV([N], [NRHS], D, E, B, [LDB], [INFO])

INTEGER :: N, NRHS, LDB, INFO
REAL(8), DIMENSION(:) :: D, E
REAL(8), DIMENSION(:,:) :: B

SUBROUTINE PTSV_64([N], [NRHS], D, E, B, [LDB], [INFO])

INTEGER(8) :: N, NRHS, LDB, INFO
REAL(8), DIMENSION(:) :: D, E
REAL(8), DIMENSION(:,:) :: B

C INTERFACE
#include <sunperf.h>

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

void dptsv_64(long n, long nrhs, double *d, double *e,  dou-
ble *b, long ldb, long *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) The order of the matrix A.  N >= 0.

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

D (input/output)
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)
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 bidiago-
nal  factor  U  from the U**T*D*U factorization of
A.)

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

INFO (output)
= 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.

```