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
infoparameter is not 0, either an error or warning was encountered. The possible return values for the
infoparameter along with the error code descriptions are given in the following table.
Problem with size of the system
Problem with size of initial subspace
i-th value of the input Extended Eigensolver parameter (
). Only the parameters in use are checked.
Successful return of only the computed subspace after call with
Size of the subspace
m0is too small (
No Convergence (number of iteration loops >
No eigenvalue found in the search interval. See remark below for further details.
Internal error for allocation memory.
Internal error of the inner system solver. Possible reasons: not enough memory for inner linear system solver or inconsistent input.
Internal error of the reduced eigenvalue solver
Possible cause: matrix
Bmay not be positive definite. It can be checked by setting
= 1before calling an Extended Eigensolver routine, or by using LAPACK routines.
Bis not positive definite.
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
or simply rescale more appropriately the search interval. Rescaling means the initial problem of finding all eigenvalues the search interval [
max] for the standard eigenvalue problem
xis replaced with the problem of finding all eigenvalues in the search interval [
t] for the standard eigenvalue problem (
tis a scaling factor.