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[FAQ]

At 18.0 it was documented that if a model has rigid body modes RangeFact should be set higher than 2 to get accurate low flexible modes. Also the following limitations were documented in the SNOPTION command notes: 1)If rigid body modes are present in the model by which you seek for rigid body modes as a solution, the accuracy of the lower flexible modes is slightly deteriorated due to rigid body modes presented and Supernode eigensolver approximation. In this case, you should increase the values of RangeFact to be higher than 2.0 (default) and smaller than 10.0 to achieve better accuracy for lower flexible modes 2)Since the Supernode is formed arbitrarily and automatically, different domain decomposition (different number of cores in DMP parallel processing) will slightly affect the solution accuracy. However, this effect of inaccuracy is normally less than 0.1 % in eigenvalues solution. 3)Supernode eigensolver does not used equation pivoting logic to process or factorize local equations. Therefore, any a finite element formulation that requires pivoting to achieve equation solution, such as element formulation with Lagrangian multipliers (U/P formulation), will not be supported (it automatically switch to Block Lanczos modal solution in this case.