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

***ERROR*** ELEMENT NUMBER P, NODE Q, VARIABLE R HAS ILLEGAL DIAGONAL DECAY = S


The most common cause of such a message is that there are 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.  More common causes on a page of related 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

Alternativley, the element numbers can be located in the model using a Labels layer:

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


Continued difficulties? Try the pivot checklist

The diagonal decay measure used in the Frontal solution method is discussed in the the following reference:

Help > Help Topics > Contents >Theory Manual Volume 1 > Section 2.2.2 Frontal Solver

More on diagonal decays 


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