Convergence Plots
Convergence plots use graphics to show how an error estimate or time step evolves during the solution process for nonlinear, time-dependent, and parametric solvers. By default, convergence plots are generated.
To control which solvers generate convergence plots, click the Convergence Plot Settings () button in The Progress Window toolbar to select or clear the convergence plots for each solver. For example, for a nonlinear time-dependent model, the menu that contains the nonlinear solver and Time-Dependent Solver (Generalized-alpha) as options.
By default, all solvers are selected, and the convergence plot for each solver appears in its own Convergence Plot window. Click to clear the check mark for a solver to turn off its convergence plot.
Click the Copy Convergence Data to Model button () in the toolbar to copy the convergence data to a table in the Table window. Clicking this button is also the only way to keep the convergence plots in model files.
NaNs (Not-a-Number entries) that appear in the tabulated convergence data represent breaks between multiple convergence cycles in an interactive solution process.
Convergence Information in the Plots
The convergence plots show an error estimate against the iteration number for the nonlinear solver and for the iterative linear system solvers (the Conjugate gradients, BiCGStab, GMRES, FGMRES, TFQMR, and multigrid solvers). See Convergence Criteria for Linear Solvers.
For the nonlinear solver, the convergence plots show an error estimate for each nonlinear iteration number. These numbers also appear in The Log Window. The segregated solver shows one plot with one graph for each segregated step.
For the iterative linear system solvers, the error estimate for each linear iteration is a factor times the relative (preconditioned) residual. This number also appears in the Log window as LinErr. When these solvers are used together with the nonlinear solver, the graphs for the different linear-system solution steps are merged, and the plots use the accumulated number of iterations. Each linear solver used has a separate plot window.
When using the parametric solver, the graphs for the different parameter steps are merged, and the convergence plots use the accumulated number of iterations. The graphs for the different nonlinear and linear solve steps are concatenated. The plot uses the accumulated number of iterations.
When using a Time-Dependent Solver, the graph in the Convergence Plot window shows the reciprocal of the time step size versus the time step. That is, a convergence plot with decreasing values shows that the time-dependent solver takes longer time steps, and vice versa.
The error estimate numbers for the last iteration also appear in the Convergence column in The Progress Window.
Changing the Default Settings
Open the Preferences dialog box and click Results to edit the preferences for the plots that you can use to monitor solver convergence.
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The Generate convergence plots check box is selected by default. Clear that check box if you do not want the software to generate convergence plots.
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To control the size of the buffer used for storing the steps in the convergence plot, in the Convergence plot buffer size (steps per plot) field (default value: 10,000 steps).