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Typical error message found in the LUSAS Solver text output file (*.OUT):

***ERROR*** PIVOT ON LEADING DIAGONAL IS ZERO. MATRIX IS SINGULAR. IS THERE A RESTRAINT AT NODAL POINT NUMBER X FOR NODAL VARIABLE NUMBER Y


Typical causes of this message are:

  1. Insufficient supports assigned to the model. It is necessary to ensure that there exist supports that restrain the entire model from rigid body movements. The model should not be free to translate or rotate freely.  
  2. Shear area or other stiffnesses set to zero.  Check your geometric attributes for stiffnesses which are zero. In general, eccentricity is the only stiffness parameter where a zero should be specified.

The error gives element numbers and these can be located in the model using

TreeView > Layers tab > Labels > (check) Element name (check) Label selected features only

and

Edit > Advanced selection

More common causes on a page of related warnings

Continued difficulties? Try the pivot checklist


More on zero pivots 


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Any modelling, design and analysis capabilities described are dependent upon the LUSAS software product, version and option in use.