Extended Eigensolver Output Details

Developer Reference for Intel® oneAPI Math Kernel Library for Fortran

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ID 766686

Date 3/31/2023

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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=λx 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.

Parent topic: Extended Eigensolver Interfaces for Eigenvalues within Interval

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Developer Reference for Intel® oneAPI Math Kernel Library for Fortran

Extended Eigensolver Output Details