A Time Dependent, Modal Reduced-Order Model node () contains settings for an online model using a time domain modal method. See Modal Reduced-Order Models.

Click Export Reduced Model () to save the reduced-order model to file as COMSOL Reduced Model file (MPHROM-file). Note that export is only possible if all defined outputs are linear quantities.

The Settings window for a Time Dependent, Modal, Reduced-Order Model node contains the following sections:

Here you specify the Time value to be used when evaluating outputs. It is by default set to t, which means that the reduced-order model will be evaluated for the same time as in the calling model in which it is used.

The list in this section contains the reduced-oder model input quantities that were set as active in the corresponding Model Reduction node’s Model Control Inputs section when the reduced-order model was created. For each model control input in the Variable column, specify a corresponding Expression to be used when evaluating outputs from the reduced-order model. The default expression is the name of the corresponding reduced-order model input variable. The effect of this setting is that the reduced-order model will be evaluated for the same value of the input as is seen by the calling model in which it is used. This is usually the desired behavior.

This section provides an overview of output quantities that the reduced-order model makes available for evaluation, both during solution and in postprocessing. These outputs are defined in the corresponding Model Reduction node’s Outputs section. The Variable column shows the variable names defined by the reduced-order model.

When Use output dependent variables is selected, the reduced-order model also declares the dependent variable names entered in the Dependent variable column. When the reduced-order model is part of another model, these dependent variables can be assigned the value of the corresponding output variable each time a solution is stored. This behavior is controlled by the Store output dependent variables setting in the Physics and Variables Selection section of each study step where the reduced-order model is used.

This section displays a list of dependent variable fields which this reduced-order model can reconstruct. When the reduced-order model is used in a calling model, it defines an operator <rom_name>.eval(<expr>), where <rom_name> is the Name of the reduced-order model and <expr> is an arbitrary expression.

Use the Load factor to scale the constant part of the right-hand side of the frequency-domain model. This in practice scales all loads and source terms with the specified factor.

Specify a Relative tolerance for the BDF time-stepping method used inside the online model.

Under Matrices, all matrices that the reduced model solution includes are listed. The listed vectors and matrices can be accessed using the COMSOL API.