Solver Setting - Tolerances

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Navigation: User Guide ➔ Menu Commands ➔ View ➔ Solver Settings ➔ Tolerances

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The Tolerances Tabs lists all tolerance values used in various solve routines.

These include both System routines and model-based routines.

The user can change values in this window to help speed up convergence.


  1. In the example shown here, most of the convergence routines use the Brent Solver.
  2. The tolerances CANNOT be set for individual unit operations, only for classes of units.
  3. Any settings which have been changed from the defaults are highlighted in yellow. Reset to default by entering *.

The methodology used by the Brent Solver to determine if a value is converged is as follows:

D = (Br1 - Br2)/2
where: Br1 and Br2 are the previous 2 results from the Brent function where they straddle the target value.
TV = 2.0 * Absolute(Br2) + RT/2
TV - Tolerance Value
RT - Relative Tolerance
Then if Absolute(D) <= TV, the routine is converged.

Related Topics: Tolerance Testing

An example is shown below:

Solver Settings-Tolerances1.jpg

Solver Settings-Tolerances2.jpg