Developer Reference

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

?gtcon

Estimates the reciprocal of the condition number of a tridiagonal matrix.

Syntax

call sgtcon
(
norm
,
n
,
dl
,
d
,
du
,
du2
,
ipiv
,
anorm
,
rcond
,
work
,
iwork
,
info
)
call dgtcon
(
norm
,
n
,
dl
,
d
,
du
,
du2
,
ipiv
,
anorm
,
rcond
,
work
,
iwork
,
info
)
call cgtcon
(
norm
,
n
,
dl
,
d
,
du
,
du2
,
ipiv
,
anorm
,
rcond
,
work
,
info
)
call zgtcon
(
norm
,
n
,
dl
,
d
,
du
,
du2
,
ipiv
,
anorm
,
rcond
,
work
,
info
)
call gtcon
(
dl
,
d
,
du
,
du2
,
ipiv
,
anorm
,
rcond
[
,
norm
]
[
,
info
]
)
Include Files
  • mkl.fi
    ,
    lapack.f90
Description
The routine estimates the reciprocal of the condition number of a real or complex tridiagonal matrix
A
in the 1-norm or infinity-norm:
κ
1
(
A
) = ||
A
||
1
||
A
-1
||
1
κ
(
A
) = ||
A
||
||
A
-1
||
An estimate is obtained for
||
A
-1
||
, and the reciprocal of the condition number is computed as
rcond
= 1 / (||
A
|| ||
A
-1
||)
.
Before calling this routine:
  • compute
    anorm
    (either
    ||
    A
    ||
    1
    = max
    j
    Σ
    i
    |
    a
    i
    j
    |
    or
    ||
    A
    ||
    = max
    i