1. But#

This command allows you to count and save (in an sd_table) the number of eigenvalues included in:

A**real axis range* (for generalized GEPs standard problems with symmetric real matrices).

A**complex plane disk* (for all other scenarios, other GEPs and all quadratic problems QEPs).

When treating standard GEPs, running this procedure generally requires only one LDLT factorization per mode. When they are scattered throughout the complex plane, the procedure is much more expensive. In this case, it is therefore rather reserved for simplified problems of small size (less than 1000 degrees of freedom).

Calling this operator is recommended as verification/calibration a priori of the model. It also makes it possible to define balanced search intervals containing a reasonable number of eigenvalues (typically a few dozen). This is in order to optimize the costs of subsequent modal operators and not to degrade the accuracy of their results.

To effectively deal with a GEP standard [1] _ , it is proposed to proceed in several steps:

  • Calibrate the areas of interest by pre-calculations using only INFO_MODE (sequentially or, if possible, in parallel) on given frequency lists (resp. critical loads);

  • Relaunch one or more CALC_MODES calculations with OPTION =” BANDE “split across several sub-bands, based on these initial calibrations.

For intensive computing, the operator INFO_MODE [2] _ , can benefit from two levels of parallelism. Time savings can reach a factor of 70 on a hundred processors, and peak memory gains a factor of 2. The implementation of parallelism is described in the dedicated section of the documentation [U2.06.01].

This operator produces a conceptsd_table.

In a first approach, you can simply fill in the parameters: MATR_ *, TYPE_MODE and FREQ (or CHAR_CRIT or*_ CONTOUR).

This operator is complementary to the operator CALC_MODES [U4.52.02].