## Developer Reference

• 2020.2
• 07/15/2020
• Public Content
Contents

# ?pttrs

Solves a system of linear equations with a symmetric (Hermitian) positive-definite tridiagonal coefficient matrix using the factorization computed by
?pttrf
.

## Syntax

Include Files
• mkl.fi
,
lapack.f90
Description
The routine solves for
X
a system of linear equations
A*X
=
B
with a symmetric (Hermitian) positive-definite tridiagonal matrix
A
. Before calling this routine, call
?pttrf
to compute the
L*D*L
T
or
U
T
*D*U
for real data and the
L*D*L
H
or
U
H
*D*U
factorization of
A
for complex data.
Input Parameters
uplo
CHARACTER*1
.
Used for
cpttrs
/
zpttrs
only. Must be
'U'
or
'L'
.
Specifies whether the superdiagonal or the subdiagonal of the tridiagonal matrix
A
is stored and how
A
is factored:
If
uplo
=
'U'
, the array
e
stores the conjugated values of the superdiagonal of
U
, and
A
is factored as
U
H
*D*U
.
If
uplo
=
'L'
, the array
e
stores the subdiagonal of
L
, and
A
is factored as
L*D*L
H
.
n
INTEGER
.
The order of
A
;
n
0.
nrhs
INTEGER
.
The number of right-hand sides, that is, the number of columns of the matrix
B
;
nrhs
0.
d
REAL
for
spttrs
,
cpttrs
DOUBLE PRECISION
for
dpttrs
,
zpttrs
.
Array, dimension (
n
). Contains the diagonal elements of the diagonal matrix
D
from the factorization computed by
?pttrf
.
e
,
b
REAL
for
spttrs
DOUBLE PRECISION
for
dpttrs
COMPLEX
for
cpttrs
DOUBLE COMPLEX
for
zpttrs
.
Arrays:
e
(
n
-1),
b