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# dpttrs

```
NAME
DPTTRS - solve a system of linear equations A * X = B with a
symmetric positive definite tridiagonal matrix A using the
factorization A = L*D*L**T or A = U**T*D*U computed by
DPTTRF

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

INTEGER        INFO, LDB, N, NRHS

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

PURPOSE
DPTTRS solves a system of linear equations A * X = B with a
symmetric positive definite tridiagonal matrix A using the
factorization A = L*D*L**T or A = U**T*D*U computed by
DPTTRF.  (The two forms are equivalent if A is real.)

ARGUMENTS
N       (input) INTEGER
The order of the tridiagonal 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) DOUBLE PRECISION array, dimension (N)
The n diagonal elements of the diagonal matrix D
from the factorization computed by DPTTRF.

E       (input) DOUBLE PRECISION array, dimension (N-1)
The (n-1) off-diagonal elements of the unit bidiago-
nal factor U or L from the factorization computed by
DPTTRF.

(LDB,NRHS)
B       (input/output) DOUBLE PRECISION array, dimension
On entry, the right hand side matrix B.  On exit,
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
```