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.h
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
matrix_layout
Specifies whether matrix storage layout is row major (
LAPACK_ROW_MAJOR
) or column major (
LAPACK_COL_MAJOR
).
uplo
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
The order of
A
;
n
0.
nrhs
The number of right-hand sides, that is, the number of columns of the matrix
B
;
nrhs
0.
d
Array, dimension (
n
). Contains the diagonal elements of the diagonal matrix
D
from the factorization computed by
?pttrf
.
e
Array
e
is of size (
n
-1).
The array
e
contains the (
n
- 1) sub-diagonal elements of the unit bidiagonal factor
L
or the conjugated values of the superdiagonal of
U
from the factorization computed by
?pttrf
(see
uplo
).
e
,
b
The array
b
contains the matrix
B
whose columns are the right-hand sides for the systems of equations.
The size of
b
is at least max(1,
ldb
*
nrhs
) for column major layout and max(1,
ldb
*
n
) for row major layout.
ldb
b
;
ldb
max(1,
n
) for column major layout and
ldb
nrhs
for row major layout
.
Output Parameters
b
Overwritten by the solution matrix
X
.
Return Values
This function returns a value
info
.
If
info
=0
, the execution is successful.
If
info
=
-i
, parameter
i