LANBOPTION,
        StrmCk
Specifies Block Lanczos eigensolver options.
StrmCkControls whether the Block Lanczos eigensolver will perform a Sturm sequence check:
OFF  | —  | Do not perform the Sturm sequence check (default).  | 
ON  | —  | Perform a Sturm sequence check. This requires additional matrix factorization (which can be expensive), but does help ensure that no modes are missed in the specified range.  | 
The Sturm sequence check is off for the Block Lanczos eigensolver when it is used in a modal analysis, and on when it is used in a buckling analysis.