AWE Solver
Use the AWE Solver () to perform fast-frequency parameter sweeps using asymptotic waveform evaluation (AWE). If, for a Frequency Domain study, the Use asymptotic waveform evaluation check box is selected under Study Extensions, or for an Adaptive Frequency Sweep study, this solver is used. It is an alternative way to perform parameter stepping to the one you get by using the Stationary Solver node in conjunction with the Parametric attribute subnode.
•
The AWE Solver Algorithm
•
AWE in the COMSOL Multiphysics Programming Reference Manual.
General
Use the Parameter name field to specify a parameter name. The use of several parameter names is not supported.
Use the Parameter values field to enter a vector of parameter values that define the parameter value span for the simulation. Exactly how the vector of parameter values is used by the solver is determined by the option Parameters to store in the Output section as described below.
Use the Asymptotic Waveform Evaluation (AWE) Expressions table to specify a space-separated list of globally available scalar-valued expressions to be used for error estimation by the AWE algorithm.
Tolerances
In the AWE algorithm, the values of the expressions specified in the Asymptotic Waveform Evaluation (AWE) Expressions table in the General section are evaluated at one or more points of a parameter interval using certain expansions. The AWE algorithm is considered to have converged in that interval if the functional values resulting from the different expansions and evaluation points are similar enough. Use the:
•
Relative tolerance field to specify to what relative tolerance the functional values must agree at the evaluation points.
•
Absolute tolerance field to specify to what absolute tolerance the functional values must agree at the evaluation points.
Expansion Settings
Use the Evaluation points field to specify a scalar or vector of values where the expressions defined by the Asymptotic Waveform Evaluation (AWE) Expressions table in the General section are to be evaluated. The evaluation points must be specified as a number between 0 and 1 because they are interpreted as being relative to the parameter interval under consideration. Entering a scalar value of 0.5 means that the expressions are evaluated at the midpoint of each interval. Use the:
•
 Expansion size list to specify the number of terms to include when performing Taylor expansions of the solution.
•
 Expansion type list to specify which expansion type to use when evaluating the solution at the different evaluation points:
-
Select Padé to compute a Padé expansion based on the Taylor expansion. The Padé expansion is then used when evaluating the solution.
-
Select Taylor to use the Taylor expansion itself when evaluating the solution.
Values of Linearization Point
The problem solved by the AWE solver is assumed to be a linearization about a solution. You can specify such a solution (a linearization point) using the Prescribed by list. Select:
•
 Initial expression to use the expressions specified on the Initial Values nodes under a specific physics interface as a linearization point.
•
 Solution to use a solution as a linearization point.
Use the Solution list to specify which solution to use if Prescribed by has been set to Solution. Select:
•
 Zero to use a linearization point that is identically equal to zero.
•
Any other available solution to use it as a linearization point. It can be the current solution in the sequence, or a solution from another sequence, or a solution that was stored with the Solution Store node. You select a stored solution by changing Use to the name of the stored solution.
To store the used linearization point in the output, select the Store linearization point and deviation in output check box.
Output
Use the Parameters to store list to control at what parameter values the solver stores a solution. Select:
•
Steps given to store solutions at the parameter values entered in the Parameter values field in the General section.
•
Steps taken by solver to store solutions at the parameter values where the AWE algorithm has performed an expansion.
If you are computing a reduced-order model, you can select the Reduced model check box to output a reduced model to a new or existing Reduced Models node that you select from the Reduced model list. If you want to use reconstruction of the original model from the reduced model, select the Enable reconstruction capability check box.
Advanced
By default the solver allows shorter intervals in the AWE algorithm than the relative tolerance (from the Relative tolerance field in the Tolerances section) times the length of the interval defined by the values in the Parameter values field in the General section. But if shorter intervals are detected, these intervals are not bisected and a warning is printed in the log. To modify the shortest allowed interval, select the Minimal interval check box and enter a limit for the interval length.
The Accept short intervals check box can be used to control how the solver handles intervals that are found to be too short. If this check box is cleared, the solver stops with an error if the interval found is too short. If you select the check box, the solver silently accepts short intervals.
Use the Assembly strategy list to control how the solver assembles quantities needed to compute a Taylor expansion. Select:
•
All to assemble all quantities at once. This option is faster than One.
•
One to assemble one quantity at a time. This option requires less memory than All.
Constants
In this section you can define constants that can be used as temporary constants in the solver. You can use the constants in the model or to define values for internal solver parameters. These constants overrule any previous definition (for example, from Global Definitions). The constant values are expressions and can, for example, include the range() operator, units, and global expressions. The constant name can be a new or an existing global parameter. The constant is temporary in the sense that it is only defined during the solver run. You cannot override parameters used in the following parts of the model:
•
Mesh and geometry
•
Selections
•
Probes
•
Functions
•
Materials
•
Pairs
•
Solver sequences
•
Parameter-dependent lists
Also, the Parametric and Time Dependent solvers overrule any definition of solver constants.
Constants settings for a solver node do not carry over to postprocessing.
Some examples of when it can be useful to define constants for a solver:
•
When doing more advanced solver sequences, where constants need to be changed between calls (for example, in for-loops).
•
When you do not want to change the global definition of a parameter or when you cannot or do not want to use a Parametric Solver feature.
•
When you want to define auxiliary parameters that are part of the equations like CFLCMP or niterCMP and where the solver does not define these parameters.
Click the Add button () to add a constant and then define its name in the Constant name column and its value (a numerical value or parameter expression) in the Constant value column. By default, any defined parameters are first added as the constant names, but you can change the names to define other constants. Click Delete () to remove the selected constant from the list.
Log
This section, which is initially empty, contains a log from the time stepping. Select the Keep warnings in stored log check box as needed.