Specifying Convergence Control |
  
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Specifying Convergence Control |
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Convergence control is specified in the Analysis Options dialog, which can be opened by clicking Analysis > Analysis Options.
When a model contains tension-only members or compression-only members, or when a P-Delta analysis is run, the analysis is an iterative process. Sometimes many iterations are required before convergence is achieved. Sometimes convergence requires too many iterations to be practical, or perhaps convergence is not even achievable. Without some control over the iteration process, this could lock up a processor in an infinite loop.
To avoid long delays and infinite loops, the program offers two controls on convergence: Maximum iterations and Axial force tolerance.
The Maximum iterations control allows the user to specify an overall maximum number of iterations that will be run when an analysis is performed. If convergence has been achieved before that number of iterations, the analysis stops when convergence has been reached. If convergence has not been achieved, the analysis stops when it reaches the specified maximum number of iterations.
The control named Axial force tolerance between P-Delta iterations sets a threshold for the program to determine if a P-Delta analysis has converged. By comparing the maximum amount of change in the axial force in any member with this specified value, the program is able to determine if the changes are small enough to consider the analysis to have converged.
