COMSOL Multiphysics™

femnlin
partial solution was returned, and 2 if no solution was returned. For the other
outputs, see femlin.
femlin and femnlin can solve a stationary problem for a number of values of a
parameter. The name of the parameter is specified with the property Pname, and the
values of the parameter is specified with the property Plist. The vector in Plist
can be an increasing or decreasing sequence of parameter values. If more than two
parameter values are given, then solutions are delivered for these parameter values
(though the algorithm may internally compute the solution for intermediate
values). If only two parameter values are given, the algorithm also delivers the
solutions for the intermediate values determined by the algorithm. The algorithm
tries to follow a continuous path of solutions when varying the parameter, and
adjusts the step size in the parameter in order achieve this. If the algorithm detects
that some sort of singularity or turning point is approached, then the stepsize is
reduced, and the algorithm terminates. In this case, if the property Stop is set to on,
the solutions for the visited parameter values are delivered.
When going from one parameter value to another, the initial guess at the new
parameter value is by default obtained by following the tangent to the solution curve
at the old parameter value. If the property Porder is set to 0, then the initial guess
is instead taken as the solution for the old parameter value. In very simple cases,
Porder = 0 may give better performance than the default Porder = 1.
The property Pinitstep specifies the initial parameter stepsize that will be tried.
The algorithm terminates if the Newton method diverges and the parameter step is
less than Pminstep. The property Pmaxstep provides an upper bound on the
parameter step. If any of the properties Pinitstep, Pminstep or Pmaxstep are 0
or not given, they are given default values.
For some applications the access to the solution at a previous parameter value is
needed. Such an application is for example contact problems with friction in
Structural Mechanics. The solution components controlled by the property
Oldcomp are treated in a separate linear solution step, or updating step, performed
after the solver for the parameter step has finished. These components are subtracted
from the solution components and are not included in the main parametric solver
step. The linear system solver used in the update solver step is UMFPACK.
For more information on the parameter-stepping feature, see “The Parametric
Solver” on page 398 in the COMSOL Multiphysics User’s Guide.
138 | CHAPTER 1: COMMAND REFERENCE