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Typical warning message from LUSAS Solver text output file (*.OUT):

***WARNING*** ELEMENT P, NODE Q, VARIABLER HAS DIAGONAL DECAY .123E+15 WHICH EXCEEDS TOLERANCE VALUE OF .10E+05


Most common causes & links to solutions 

This message points to a specific element P, node Q and degree of freedom R relative to global axes (eg. variable 6 => THZ rotational freedom). The warning is often related to high differences in stiffness between the elements and/or boundary conditions at this node. For example, where a very stiff element connects with much less stiff element, a small force on one element will cause a relatively large deformation, whereas the same force on the other element will cause a relatively small deformation. For extremes of this example, large diagonal decay is reported and the stiffness matrix will become ill-conditioned. Although a check would always be recommended for any warning of this description, significant effects would not generally be expected until the decay reaches a value of 0.1E8 or greater. 

The diagonal decay message is reported when the LUSAS standard Frontal solver is used.  The Multi-Frontal Fast Solvers work in a different way and therefore do not report diagonal decay warnings.

To use the LUSAS Frontal Solver for the purpose of checking diagonal decays try File > Model properties > Solution tab > Solver options > Type: Frontal and then solve the model. 

Please also see:

Help > Help Topics > Contents > Modeller Reference Manual > Appendix B : LUSAS Solver Trouble Shooting>LUSAS Solver Errors>Diagonal Decay Warnings

How to find the target Node or Element: 

Solver error or warning messages are also scanned from Solver .out file and reported in Modeller Text Output window. By default the Text Output window appears at the bottom of the graphics window just above the Status Bar. This displays messages and warnings during a modelling session. Specific objects referred to in error and diagnostic messages in the text window by ID number in the form "Element P" may be identified using the identify object dialog. The Identify Object" dialog is invoked by double clicking on the message text. From this dialog the identified object may be selected, moved to the centre of the screen, scaled to fill the screen, have its properties displayed, or identified by an annotation arrow or a temporary indicator.

Element P can also be located in the model using Advanced Selection, activated by right- clicking with the mouse in the graphics window, or via:

Edit > Advanced Selection


More on the diagonal decay measure used in the Frontal solution method


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