# EIGVRETRIEVE

Subcase Information Entry The EIGVRETRIEVE command can be used in the Subcase Information section of Modal Frequency Response or Modal Transient Response analysis to retrieve eigenvalue and eigenvector results of a previously run Normal Modes, Modal Frequency Response, or Modal Transient Analysis from an external data file (.eigv).

## Format

EIGVRETRIEVE = `integer1`,
`integer2`, `integer3`, ...

## Definitions

Argument | Options | Description |
---|---|---|

integer# |
<integer> No default |
Retrieves eigenvalues and
eigenvectors from external data files for use in a Modal Frequency
Response or Modal Transient Response Analysis. The external eigenvalue and eigenvector data file name is of the form: <prefix>.#.eigv |

## Comments

- Only one occurrence of EIGVRETRIEVE per subcase is permitted.
- When multiple integer arguments are provided, eigenvalues are retrieved from multiple external data files and combined.
- If EIGVRETRIEVE is not present, eigenvalue and eigenvector results are not retrieved from external data files and a normal modes analysis is performed for the modal frequency response or modal transient response analysis subcase.
- In the case of an
EIGVRETRIEVE run with Modal Frequency Response or Modal
Transient Analysis:
- If partial-model eigenvectors are saved via EIGVSAVE, then EIGVRETRIEVE can be used only with AMSES (EIGRA) and AMLS eigen solvers.
- If full-model eigenvectors are saved via EIGVSAVE, then EIGVRETRIEVE can be used with Lanczos (EIGRL), AMSES (EIGRA), and AMLS eigen solvers.

- There are several scenarios under
which EIGSAVE and EIGVRETRIEVE can be used
for Modal Frequency Response and Modal Transient Analysis. Recommended
approaches for two of the most common use cases are as follows:
- Save partial model eigenvectors in .eigv file:
Saving eigenvectors only for a partial set of degrees of freedom in the
.eigv file during the
EIGVSAVE run can help improve performance. This
approach is feasible if you need to request output for only these
partial degrees of freedom (or a subset of them) in the
EIGVRETRIEVE run.
- Currently the only approach for saving eigenvectors for partial degrees of freedom in the EIGVSAVE run is by using AMSES and DISP=SET (where SET represents the degrees of freedom for which eigenvectors need to be saved in the *.eigv file).
- The type of EIGVSAVE analysis depends on how
RESVEC generation is handled, which in
turn depends on the type of loading that will be used during the
EIGVRETRIEVE run. AMSES can still be used
in EIGVRETRIEVE run. For instance:
- If FORCE load is applied in
EIGVRETRIEVE run, the
EIGVSAVE run is recommended to be
a Normal Modes analysis.
RESVEC=YES can
be defined along with USET consisting
of the corresponding FORCE dofs. This
saves the unit-load RESVECs in the
*.eigv file.Note: An alternative approach is to have the EIGVSAVE run be a full setup Modal FRF/Transient analysis with the corresponding FORCE loads applied. However, this involves additional runtime when compared to the recommended normal modes EIGVSAVE run).
- If SPCD load is applied in EIGVRETRIEVE run, the EIGVSAVE run should be a full setup Modal Frequency Response or Modal Transient analysis (similar to the EIGVRETRIEVE run). The unit-displacement RESVECs required for SPCD load in EIGVRETRIEVE run can only be calculated by a EIGVSAVE run with full-setup Modal Frequency or Modal Transient analysis (instead of a Normal Modes analysis, which only can generate unit-load RESVECs). In the EIGVRETREIVE run with SPCD, retain the SPCDs on all EIGVSAVE SPCD dofs. Otherwise, the modal space will change and the EIGVSAVE modal space cannot be used for this EIGVRETRIEVE run). However, you can change the applied SPCD constraint value on these dofs to a different value or set them to zero.
- If distributed static loads via PLOADi/GRAV/RFORCE are applied in EIGVRETREIVE run, the partial eigenvectors option is not allowed. In this case, refer to the next use case.

- If FORCE load is applied in
EIGVRETRIEVE run, the
EIGVSAVE run is recommended to be
a Normal Modes analysis.
RESVEC=YES can
be defined along with USET consisting
of the corresponding FORCE dofs. This
saves the unit-load RESVECs in the
*.eigv file.

- Save full model eigenvectors in .eigv file: Saving
eigenvectors for a full set of degrees of freedom in the
.eigv file during the
EIGVSAVE may require more runtime than requesting
a partial set of eigenvectors. However, it may be required as part of
the application use case or selected loading. With this approach, you
can request output for all degrees of freedom in the
EIGVRETRIEVE run.
- The recommended approach for saving eigenvectors for full
degrees of freedom in the EIGVSAVE run is by
using AMSES and DISP=ALL
(wherein all eigenvectors are saved in the
*.eigv file).Note: An alternative approach is to use Lanczos in EIGVSAVE run to save the full eigenvectors set, but using AMSES may provide better performance.
- Since the full set of eigenvectors are saved in the *.eigv file during EIGVSAVE run, the recommended simple approach is to use Lanczos for the EIGVRETRIEVE run. This way, RESVECs are recalculated in the EIGVRETRIEVE run and do not need to be included in the *.eigv file during EIGVSAVE run. This also works consistently for any type of loading in EIGVRETRIEVE run (FORCE, SPCD, or distributed loading via PLOADi/GRAV/RFORCE).

- The recommended approach for saving eigenvectors for full
degrees of freedom in the EIGVSAVE run is by
using AMSES and DISP=ALL
(wherein all eigenvectors are saved in the
*.eigv file).

- Save partial model eigenvectors in .eigv file:
Saving eigenvectors only for a partial set of degrees of freedom in the
.eigv file during the
EIGVSAVE run can help improve performance. This
approach is feasible if you need to request output for only these
partial degrees of freedom (or a subset of them) in the
EIGVRETRIEVE run.