The Automatic method for
Check error estimate for direct linear solvers and for
Validate error estimate has changed. For nonlinear and time-dependent problems, the underlying nonlinear solver does not accept termination for a linear solution step that does not fulfill the error estimate (unless the step size is very small). The motivation for this change is that the old method can lead to premature termination of the nonlinear solution process, which in some cases introduces a large error for the computed solution.
The default termination criterion for stationary solvers has changed. In 4.3a, the settings corresponded to Solution; now, the default is
Solution or residual. This change in default termination criterion might affect models created in earlier versions of COMSOL Multiphysics if you regenerate the solver sequence in 5.2a.
A new setting in the Advanced section of the settings window for the
Time-Dependent Solver, called
Fraction of initial step for Backward Euler, provides an option for entering a dimensionless quantity that determines the size of the time step for the backward Euler method (in terms of the initial step). This value can improve the accuracy of the initialization step but can also affect the start-up of some models. The default value is 0.001 (this differs from earlier versions, which used a value of 1). When opening models created in version 4.3a or earlier, the value for this fraction is set to 1 to maintain compatibility with those versions.