Developer Reference

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

Extended Eigensolver Output Details

Errors and warnings encountered during a run of the Extended Eigensolver routines are stored in an integer variable,
info
. If the value of the output
info
parameter is not 0, either an error or warning was encountered. The possible return values for the
info
parameter along with the error code descriptions are given in the following table.
Return Codes for info Parameter
info
Classification
Description
202
Error
Problem with size of the system
n
(
n
0)
201
Error
Problem with size of initial subspace
m0
(
m0
0 or
m0
>
n
)
200
Error
Problem with
emin
,
emax
(
emin
emax
)
(100+
i
)
Error
Problem with
i
-th value of the input Extended Eigensolver parameter (
fpm
(
i
)
). Only the parameters in use are checked.
4
Warning
Successful return of only the computed subspace after call with
fpm
(14)
= 1
3
Warning
Size of the subspace
m0
is too small (
m0
<
m
)
2
Warning
No Convergence (number of iteration loops >
fpm
(4)
)
1
Warning
No eigenvalue found in the search interval. See remark below for further details.
0
Successful exit
-1
Error
Internal error for allocation memory.
-2
Error
Internal error of the inner system solver. Possible reasons: not enough memory for inner linear system solver or inconsistent input.
-3
Error
Internal error of the reduced eigenvalue solver
Possible cause: matrix
B
may not be positive definite. It can be checked by setting
fpm
(28)
= 1
before calling an Extended Eigensolver routine, or by using LAPACK routines.
-4
Error
Matrix
B
is not positive definite.
-(100+
i
)
Error
Problem with the
i
-th argument of the Extended Eigensolver interface.
In some extreme cases the return value
info
=1 may indicate that the Extended Eigensolver routine has failed to find the eigenvalues in the search interval. This situation could arise if a very large search interval is used to locate a small and isolated cluster of eigenvalues (i.e. the dimension of the search interval is many orders of magnitude larger than the number of contour points. It is then either recommended to increase the number of contour points
fpm
(2)
or simply rescale more appropriately the search interval. Rescaling means the initial problem of finding all eigenvalues the search interval [
λ
min
,
λ
max
] for the standard eigenvalue problem
A x
=
λ
x
is replaced with the problem of finding all eigenvalues in the search interval [
λ
min
/
t
,
λ
max
/
t
] for the standard eigenvalue problem (
A
/
t
)
x
=(
λ
/
t
)
x
where
t
is a scaling factor.