Developer Reference

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

?stebz

Computes selected eigenvalues of a real symmetric tridiagonal matrix by bisection.

Syntax

call sstebz
(
range
,
order
,
n
,
vl
,
vu
,
il
,
iu
,
abstol
,
d
,
e
,
m
,
nsplit
,
w
,
iblock
,
isplit
,
work
,
iwork
,
info
)
call dstebz
(
range
,
order
,
n
,
vl
,
vu
,
il
,
iu
,
abstol
,
d
,
e
,
m
,
nsplit
,
w
,
iblock
,
isplit
,
work
,
iwork
,
info
)
call stebz
(
d
,
e
,
m
,
nsplit
,
w
,
iblock
,
isplit
[
,
order
]
[
,
vl
]
[
,
vu
]
[
,
il
]
[
,
iu
]
[
,
abstol
]
[
,
info
]
)
Include Files
  • mkl.fi
    ,
    lapack.f90
Description
The routine computes some (or all) of the eigenvalues of a real symmetric tridiagonal matrix
T
by bisection. The routine searches for zero or negligible off-diagonal elements to see if
T
splits into block-diagonal form
T
= diag(
T
1
,
T
2
, ...)
. Then it performs bisection on each of the blocks
T
i
and returns the block index of each computed eigenvalue, so that a subsequent call to stein can also take advantage of the block structure.
See also laebz.
Input Parameters
range
CHARACTER*1
.
Must be
'A'
or
'V'
or
'I'
.
If
range
=
'A'
, the routine computes all eigenvalues.
If
range
=
'V'
, the routine computes eigenvalues
w
(
i
)
in the half-open interval:
vl
<
w
(
i
)
vu
.
If
range
=
'I'
, the routine computes eigenvalues with indices
il
to
iu
.
order
CHARACTER*1
.
Must be
'B'
or
'E'
.
If
order
=
'B'
, the eigenvalues are to be ordered from smallest to largest within each split-off block.
If
order
=
'E'
, the eigenvalues for the entire matrix are to be ordered from smallest to largest.
n
INTEGER
.
The order of the matrix
T
(
n
0
).
vl
,
vu
REAL
for
sstebz
DOUBLE PRECISION
for
dstebz
.
If
range
=
'V'