Developer Reference

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

?gttrf

Computes the LU factorization of a tridiagonal matrix.

Syntax

call sgttrf
(
n
,
dl
,
d
,
du
,
du2
,
ipiv
,
info
)
call dgttrf
(
n
,
dl
,
d
,
du
,
du2
,
ipiv
,
info
)
call cgttrf
(
n
,
dl
,
d
,
du
,
du2
,
ipiv
,
info
)
call zgttrf
(
n
,
dl
,
d
,
du
,
du2
,
ipiv
,
info
)
call gttrf
(
dl
,
d
,
du
,
du2
[
,
ipiv
]
[
,
info
]
)
Include Files
  • mkl.fi
    ,
    lapack.f90
Description
The routine computes the
LU
factorization of a real or complex tridiagonal matrix
A
using elimination with partial pivoting and row interchanges.
The factorization has the form
A
=
L*U
,
where
L
is a product of permutation and unit lower bidiagonal matrices and
U
is upper triangular with nonzeroes in only the main diagonal and first two superdiagonals.
Input Parameters
n
INTEGER
.
The order of the matrix
A
;
n
0.
dl
,
d
,
du
REAL
for
sgttrf
DOUBLE PRECISION
for
dgttrf
COMPLEX
for
cgttrf
DOUBLE COMPLEX
for
zgttrf
.
Arrays containing elements of
A
.
The array
dl
of dimension
(
n
- 1)
contains the subdiagonal elements of
A
.
The array
d
of dimension
n
contains the diagonal elements of
A
.
The array
du
of dimension
(
n
- 1)
contains the superdiagonal elements of
A
.
Output Parameters
dl
Overwritten by the
(
n
-1)
multipliers that define the matrix
L
from the
LU
factorization of
A
.
The matrix
L
has unit diagonal elements, and the
(
n
-1)
elements of
dl
form the subdiagonal. All other elements of
L
are zero.
d
Overwritten by the
n
diagonal elements of the upper triangular matrix
U
from the
LU
factorization of
A
.
du
Overwritten by the
(
n
-1)
elements of the first superdiagonal of
U
.
du2
REAL
for
sgttrf
DOUBLE PRECISION
for
dgttrf
</