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This page is devoted to frequently asked questions (FAQ) related to numerical problems.

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Table of Contents

What does the Lost Accuracy warning message indicate, and how is it resolved?

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Answer: Lost accuracy applies to the stiffness matrix and its values during numerical solution. Since stiffness governs the relationship between force and displacement, lost accuracy will affect both of these response measures.

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I received a body-constraint lost-accuracy warning message. How is this calculated?

Answer: Body and other rigid constraints create an internal master node which governs the nodes assigned to the constraint. These master nodes become part of the system of equations while the constrained nodes do not. When lost accuracy occurs within the constraint, it is reported for the master node, and not the individual components.


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What causes the numerical problem Diagonal < 0, and how is it resolved?

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Possible causes:

  • For linear analysis, Diagonal < 0 could result from an , in which constrained points are not exactly on the edge.
  • See 9/2/2010 email from fs, ID 3705068
  • For analysis, when effect is considered, negative terms may occur on the diagonal of the stiffness matrix at the onset of .
  • See Incident 27490 - example of Diagonal < 0 numerical problem.

What is the difference between equation-assembly and equation-solution numerical problems?

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