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# cpttrs

```
NAME
CPTTRS - solve a system of linear equations A * X = B with a
Hermitian positive definite tridiagonal matrix A using the
factorization A = U**H*D*U or A = L*D*L**H computed by
CPTTRF

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

CHARACTER      UPLO

INTEGER        INFO, LDB, N, NRHS

REAL           D( * )

COMPLEX        B( LDB, * ), E( * )

PURPOSE
CPTTRS solves a system of linear equations A * X = B with a
Hermitian positive definite tridiagonal matrix A using the
factorization A = U**H*D*U or A = L*D*L**H computed by
CPTTRF.

ARGUMENTS
UPLO    (input) CHARACTER*1
Specifies whether the superdiagonal or the subdiago-
nal of the tridiagonal matrix A is stored and the
form of the factorization:
= 'U':  E is the superdiagonal of U, and A = U'*D*U;
= 'L':  E is the subdiagonal of L, and A = L*D*L'.
(The two forms are equivalent if A is real.)

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) REAL array, dimension (N)
The n diagonal elements of the diagonal matrix D
from the factorization computed by CPTTRF.

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

B       (input/output) REAL array, dimension (LDB,NRHS)
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
```