Dependent Variables
The Dependent Variables node () handles initial data and scaling for the dependent variables that you solve for as well as how to compute dependent variables not solved for. The methods are applicable to the dependent variables present as Field subnodes () under the Dependent Variables node. The Field node name matches the name of the variable.
To plot and evaluate the initial values for the dependent variables, right-click the Dependent Variables node and choose Compute to Selected () or click the button on the toolbar (this is similar to the Get Initial Value option for the main Study nodes).
The Settings window has the following sections:
General
Use the Defined by study step list to specify if the settings are synchronized with the corresponding study step. Select User defined to specify all settings locally in the Dependent Variable node’s Settings window. This setting relates to the Field node’s setting to Solve for this field.
Initial Values of Variables Solved For
This section is only available if you select User defined from the Defined by study step list.
Use the Method list to specify how to compute initial values for the dependent variables that you solve for. Select:
Initial expression (the default) to use the expressions specified on the Initial Values nodes for the physics interfaces in the model.
Solution to use initial values as specified by a solution object. Use the Solution list to specify what solution object to use (directly or as part of the initial expression). Select:
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Zero to initialize all variables to zero.
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Solution List Options by Study Type
Depending on the study type for the selected solution object, you can choose different solutions from a list underneath the Solution list:
For a Stationary study, from the Selection list, select Automatic (the default) to use the last (typically the only) solution, select First to use the first (typically the only) solution, select Last to use the last (typically the only) solution, select All to use all (typically just one) solutions from that study, select Manual to use a specific solution number that you specify, or select 1 to use the first (typically the only) solution. If you use a parametric continuation of the stationary study, there can be additional solutions to choose from.
For a Time Dependent study, from the Time list, select Automatic (the default) to use the solution for the last time, select First to use the first solution, select Last to use the last solution, select All to use all solutions from that study, select Interpolated to specify a time in the text field that opens and use the interpolated solution at that time, select Manual to use a specific solution number that you specify, or select one of the output times to use the solution at that time.
For an Eigenvalue study, from the Selection list, select Automatic (the default) to use the first eigenvalue and its associated eigensolution, select First to use the first solution, select Last to use the last solution, select All to use all solutions from that study, select Manual to use a specific solution number that you specify, or select one of the eigenvalues to use the corresponding eigensolution.
For a Parametric Sweep or Frequency Domain study, from the Parameter value list, select Automatic (the default) to use the first parameter value set or frequency, select First to use the first solution, select Last to use the last solution, select All to use all solutions from that study, select Manual to use a specific solution number that you specify, or select one of the parameter value sets or frequencies to use the corresponding solution.
Scaling
Use the Method list to specify how to scale the variables solved for. Select:
Automatic to get an automatically determined scaling (the default), which works well for most models. It is initially based on the magnitudes of the elements in the Jacobian and mass matrices. For nonlinear problems these scales are recomputed based on the magnitude of the solution iterate.
Initial value based to get a scaling that is determined from the initial values. Use this if the components of the initial values give a good estimate of the order of magnitude of the solution.
Manual to manually enter a scaling if you know the order of magnitudes of the variables in advance. For instance, suppose that a model solves for a dependent variable u, and that the values of u are on the order of 104. To use this knowledge, type 1e-4 in the Scale field. The solvers then internally use a solution vector rescaled to the order of 1 for u. If there is more than one dependent variable that the model solves, they are all rescaled with the same factor.
None to skip scaling.
The scaling method also can be specified for each dependent variable in the Settings window for the variable’s Field node. For more information about scaling, see Scaling of Variables and Equations.
Values of Variables Not Solved For
This section is only available if you select User defined from the Defined by study step list.
These settings are only applicable if there are dependent variables in the model that you do not solve for (in the case, for example, when solving a multiphysics model using a sequential approach). Then use the Method list to specify how to compute the values of variables not solved for. Select:
Initial expression to use the expressions specified on the Initial Values nodes for the physics interfaces in the model.
Solution to use initial values as specified by a solution object. Use the Solution list to specify what solution object to use if Method has been set to Solution. Select:
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Zero to initialize all variables to zero.
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Depending on the solution object to use, you can choose different solutions to use. If a solution has nodes for storing solutions in its sequence, you can choose which solution to use using the Use list. The Current value is the value that the solution has at the moment the value is read. The other values are the values stored in the respective nodes of the sequence.
See Solution List Options by Study Type for additional choices based on study type and then available in this section.
You select whether to solve for a variable or not by left-clicking a Field subnode () and then select or clear the Solve for this field check box in the Settings window.
Initial Value Calculation Constants
The settings in this section makes it possible to control values of parameters in models when used as constants in initial values. By default, those values are controlled automatically by the study step, and the settings are not available unless you choose User defined from the Defined by study step list in the General section above. The value is updated as soon as a subsequent solver gets its times, frequencies, or parameter lists updated. The value for each parameter is the first value in each list. You can override this automatic behavior by choosing Manual from the Parameters list. You can then add parameters as constants to the Constant name column and the corresponding initial value as a parameter expression in the Initial value source column. The constants defined here must be used in an initial value expression for the dependent variables.