SNOPTION
SNOPTION, RangeFact, BlockSize, RobustLev, Compute, --, Solve_Info
Specifies Supernode (SNODE) eigensolver options.
RangeFactFactor used to control the range of eigenvalues computed for each supernode. The value of
RangeFactmust be a number between 1.0 and 10.0. By default theRangeFactvalue is set to 2.0, which means that all eigenvalues between 0 and 2*FREQEare computed for each supernode (whereFREQEis the upper end of the frequency range of interest as specified on the MODOPT command). As theRangeFactvalue increases, the eigensolution for the SNODE solver becomes more accurate and the computational time increases.BlockSizeBlockSizeto be used when computing the final eigenvectors. The value ofBlocksizemust be either MAX or a number between 1 andNMODE, whereNMODEis the number of modes to be computed as set on the MODOPT command. Input a value of MAX to force the algorithm to allocate enough memory to hold all of the final eigenvectors in memory and, therefore, only read through the file containing the supernode eigenvectors once. Note that this setting is ONLY recommended when there is sufficient physical memory on the machine to safely hold all of the final eigenvectors in memory.RobustLevParameter used to control the robustness of the SNODE eigensolver. The value of
RobustLevmust be a number between 0 and 10. Lower values ofRobustLevallow the eigensolver to run in the most efficient manner for optimal performance. Higher values ofRobustLevoften slow down the performance of the eigensolver, but can increase the robustness; this may be desirable if a problem is detected with the eigensolver or its eigensolution.ComputeKey to control which computations are performed by the Supernode eigensolver:
EVALUE
—
The eigensolver computes only the eigenvalues.
EVECTOR
—
The eigensolver computes only the eigenvectors (must be preceded by a modal analysis where the eigenvalues were computed using the Supernode eigensolver).
BOTH
—
The eigensolver computes both the eigenvalues and eigenvectors in the same pass (default).
--Unused field
Solve_InfoSolver output option:
OFF
—
Turns off additional output printing from the Supernode eigensolver (default).
PERFORMANCE
—
Turns on additional output printing from the Supernode eigensolver, including a performance summary and a summary of file I/O for the Supernode eigensolver. Information on memory usage during assembly of the global matrices (that is, creation of the Jobname.full file) is also printed with this option.
Command Default
RangeFact = 2.0. BlockSize is
set to min(NMODE,40), where NMODE is
the number of modes to be computed as set on the MODOPT command. RobustLev =
0. Compute = BOTH. Additional output is not printed
(Solve_Info = OFF).
Notes
This command specifies options for the Supernode (SNODE) eigensolver.
Setting RangeFact to a value between 2.0 and
10.0 will improve the accuracy of the computed eigenvalues and eigenvectors, but will often
increase the computing time of the SNODE eigensolver. Conversely, setting
RangeFact to a value less than 2.0 will deteriorate the accuracy of
the computed eigenvalues and eigenvectors, but will often speed up the computing time of the
SNODE eigensolver. The default value of 2.0 has been set as a good blend of accuracy and
performance. If the model has rigid body modes, setting RangeFact
higher than 2 is recommended to achieve better solution accuracy for the lower flexible
modes.
The SNODE eigensolver reads the eigenvectors and related information
for each supernode from a file and uses that information to compute the final
eigenvectors. For each eigenvalue/eigenvector requested by the user, the
program must do one pass through the entire file that contains the supernode
eigenvectors. By choosing a BlockSize value greater
than 1, the program can compute BlockSize number
of final eigenvectors for each pass through the file. Therefore, smaller
values of BlockSize result in more I/O, and larger
values of BlockSize result in less I/O. Larger
values of BlockSize also result in significant
additional memory usage, as BlockSize number of
final eigenvectors must be stored in memory. The default Blocksize of
min(NMODE,40) is normally a good choice to balance
memory and I/O usage.
The RobustLev field should only be used when
a problem is detected with the accuracy of the final solution or if the Supernode
eigensolver fails while computing the eigenvalues/eigenvectors. Setting RobustLev to
a value greater than 0 will cause the performance of the eigensolver to deteriorate.
If the performance deteriorates too much or if the eigensolver continues to
fail when setting the RobustLev field to higher
values, then switching to another eigensolver such as Block Lanczos or PCG
Lanczos is recommended.
Setting Compute = EVALUE causes the Supernode eigensolver to
compute only the requested eigenvalues. During this process a
Jobname.SNODE file is written; however, a
Jobname.mode file is not written. Thus, errors will likely occur in any
downstream computations that require the Jobname.mode file (for example,
participation factor computations, mode superpostion transient/harmonic analysis, PSD
analysis). Setting Compute = EVECTOR causes the Supernode
eigensolver to compute only the corresponding eigenvectors. The
Jobname.SNODE file and the associated Jobname.full
file are required when requesting these eigenvectors. In other words, the eigenvalues must
have already been computed for this model before computing the eigenvectors. This field can be
useful in order to separate the two steps (computing eigenvalues and computing
eigenvectors).
For more information on the eigensolver's accuracy and a discussion of its known limitations, see Supernode Method in the Mechanical APDL Theory Reference