Use a Parametric Sweep (
) study to find the solution to a sequence of stationary or time-dependent problems that arise when you vary some parameters of interest. The parametric sweep can include multiple independent parameters directly for a full multiparameter sweep (solve for the first value of the first parameter combined with all values of the second parameter, then the second value of the first parameter combined with all values of the second parameter, and so on, or use a specified combination of parameter values). You can also add more than one
Parametric Sweep node to create nested parametric sweeps. The inner sweep in a nested parametric sweep can also be another type of sweep, such as a sweep over materials by adding a
Material Sweep node below the
Parametric Sweep node. The program then treats the parametric sweeps as a “nested for-loop” and indicates the nested structure using indentations of the sweep nodes’ names.
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See Table Surface for information about how to plot the variation of some quantity as a function of two parameters as a 2D surface plot where you vary two parameters and fix the others.
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It is only possible to use one Sensitivity or Optimization study step feature in any study, unless there is an Optimization study step, in which case you can combine the Optimization study step with one or more Parametric Sweep study steps; however, you cannot have an Optimization study step over a Parametric Sweep study step, if a gradient-based method is used. You can use several Parametric Sweep nodes if desired, but they cannot be combined with the other study step types.
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The Settings window has the following sections:
Use the Sweep type list to specify the type of sweep to perform. The
Specified combinations type (the default) solves for a number of given combinations of values, while the
All combinations type solves for all combinations of values. Using all combinations can lead to a very large number of solutions. The
Parameter switch type makes it possible to run sweeps over selected parameter groups and associated parameter cases (see
Parameters and
Parameter Cases). Using the
Parameter switch sweep type, you can run specified sweeps for all or selected parameter cases for a parameter group, and if you have more than one parameter group, you might want to compute all combinations of these groups. You can do so by setting up a complete parameter list as an outer sweep with all parameter groups and their parameter cases in the parameter switch table (see below). The
Parameter switch sweep type can also be combined with other parametric sweeps using any sweep type.
For Specified combinations and
All combinations, use the table with
Parameter name,
Parameter value list, and (optional)
Parameter unit to specify parameter names, values, and units for the parametric solver. Use the
Add button (
) to add a row to the table. Each row has one parameter name, a corresponding parameter value list, and an optional unit. The unit becomes orange if the unit that you specify does not match the unit given for the parameter where it is defined. For the
Specified combinations sweep type, the list of values must have equal length. When you click in the
Parameter value list column to define the parameter values, you can click the
Range button (
) to define a range of parameter values. The parameter unit overrides the unit of the global parameter. If no parameter unit is given, parameter values without explicit dimensions are considered dimensionless.
For Parameter switch, add parameters to switch by clicking the
Add button (
) to add a
Parameters node in the
Switch column for which to switch its parameters. In the
Cases column, choose the parameter cases to include. The default is
All (also when there are no parameter cases); choose
User defined to specify the parameter cases to include under
Case numbers. Then, during postprocessing, you can choose from the specified case numbers in lists for the added
Parameters nodes under the
Dataset list in the
Data sections for plots and data evaluations. Use the
Move Up (
),
Move Down (
), and
Delete (
) buttons as needed to rearrange the list of
Parameters nodes for a parameter switch.
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The list of parameters in the Parameter name column contains parameters from Parameters nodes where the Show in parameter selections check box is selected.
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If more than one parameter name has been specified, the lists of parameter values are interpreted as follows: Assume that the parameter names are p1 and
p2, and that
p1 has the list 1 3 and
p2 has the list 2 4. For the
Specified combinations sweep type, the solver first uses
p1 equal to
1 and
p2 equal to
2. Thereafter, it uses
p1 equal to
3 and
p2 equal to
4. And when the sweep type is
All combinations, the solver uses the following order for the parameter combinations: 1 2, 1 4, 3 2, and 3 4.
An alternative to specifying parameter names and values directly in the table is to specify them in a text file. Use the Load from File button (
) to browse to such a text file. You can also click the downward arrow beside the
Load from File button and choose
Load From (
) to open the fullscreen
Select File window. The program appends the read parameter names, values, and units to the current table. The format of the text file must be such that the parameter names appear in the first column, and the values for each parameter appear in the next columns, comma separated (
1,3,5) or separated with a space, row-wise enclosed with quotation marks and with spaces separating the values (such as "
1 3 5"). Finally (separated by a space), the format includes an optional unit using unit syntax such as
[m/s]. Click the
Save to File button (
) to save the contents of the table to a text file (or to a Microsoft Excel Workbook spreadsheet if the license includes LiveLink™
for Excel®).
You can use the Keep solutions list under
Memory settings for jobs to control how to store the solutions from the individual parametric sweep solutions. Select
All to store all the parametric sweep solutions in memory, or select
Only last to store only the last solution from the parametric sweep. If you select
Only last and the parametric solver is used, all solutions are kept in memory. When only the last solution is stored, you can also select the
Save each solution as model file check box. It stores the separate parametric sweep solutions and their corresponding models in separate MPH-files. Enter a filename in the
Filename field or click
Browse to choose a name and location for the model files. Click the downward arrow for the
Location menu (
) to choose
Copy Location (
) and (if you have copied a file location)
Paste Location (
). You can also use probes to collect some solution values of interest during the sweep rather than storing all solutions, which can save memory and solution time.
Select the Plot check box to allow plotting of results while solving. Then select what to plot from the
Plot group list. The software plots the dataset of the selected plot group as soon as the results become available.
Use the Probes list to select probes to update during the parametric sweep. The default is
All, which selects all probes for plotting and tabulation of probe data. Select
Manual to open a list with all available probes. Use the
Move Up (
),
Move Down (
),
Delete (
), and
Add (
) buttons to make the list contain the probes that you want to see results from while solving. Select
None to disable probe updating for parametric sweep. Note that the control of tables and plot windows is done using the probe settings.
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If a probe is updated on the Parametric Sweep level and also through another solution process (for example, a time-dependent simulation) this probe is not updated at the Parametric Sweep level. When the probes themselves (not the probe expression) depend on model parameters, the update of these probes is only correct for parameter sweeps that are done through outer parametric sweeps (not by a parametric solver). Outer parametric sweeps are performed by a Parametric node under Job Configurations. COMSOL Multiphysics currently does not autodetect model parameters in probes, so you might want to select Off from the Use parametric solver list in the Study Extensions section for the Parametric Sweep study node.
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Select the Accumulated probe table check box to activate the accumulation of probe updates for both the variation on the solver level (time, frequency, and so forth) and on the parametric sweep level. Use the
Output table to select where to put the data. Select the
Use all probes check box if all the model probes should be accumulated in the table. If not selected, the probes selected from the
Probes list are used.
The Keep reduced-order models check box is selected by default. Then, these additional settings are available:
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From the Add to tag list, choose Parameter name and value (the default), Index, or Parameter name and nonzero value (the latter option discards all zero values).
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The Clear previous check box is selected by default to clear previous versions of the reduced-order models so that you can update all reduced-order models by running the study again.
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The Keep the generating reduced-order models check box is selected by default. If selected, the generating reduced-order models are saved in addition to the reduced-order model copies.
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From the Use parametric solver list, select one of the following options:
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Automatic (the default) to generate a Parametric job configuration, unless the problem and parameters are such that the parametric sweep can be realized through a Stationary Solver with a Parametric solver subnode ( ), which is more efficient.
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Off to always generate a Parametric job configuration.
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From the Default solver sequence generation list, select one of the following options:
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Using global parameters (the default), to use parameter values from the global parameters.
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Using first parameter tuple, to use the first set of parameter values.
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Using last parameter tuple, to use the last set of parameter values.
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Using each parameter tuple, to use the all sets of parameter values.
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From the Default solver sequence generation list you can control when a solver sequence should be generated during a parametric sweep (see also the settings for the
Solution node under
Job Configurations):
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Choose Using global parameters (the default).
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Choose Using first parameter tuple, Using last parameter tuple, or Using each parameter tuple to instead use the first tuple (set) of parameter values, the last tuple of parameter values, or each tuple of parameter values to control when a solver sequence should be generated.
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Select the Reuse solution from previous step check box, if you want to reuse the converged values of variables from the previous sweep step as initial condition for the next step during the sweep. If a Parametric Sweep study step wraps an Optimization study step, select this check box to reuse variables solved for (both control variables and PDE variables) from the previous converged optimization call. This option is useful for parameters not handled with continuation. See
Reuse Solution from Previous Step List for information about reusing solutions.
If you are running a parametric sweep and want to distribute it by sending one parameter value to each compute node, select the Distribute parametric sweep check box. To enable this option, click the
Show More Options button (
) and select
Solver and Job Configurations in the
Show More Options dialog box. Note that if the
Distribute parametric sweep check box is selected,
Solution under
Initial values of variables solved for in the
Values of Dependent Variables section in the study step node’s settings cannot be set to
Current. Each node is assigned disjoint sets of parameters; hence, the initial solution is undefined for all nodes other than the first.
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In order for the Distribute parametric sweep check box to function, you must start COMSOL with a setup for running COMSOL on clusters or other multicore system using, for example, comsol -nn 2 -nnhost 2 on Linux ® or mpiexec -n 2 comsolcluster.exe -nnhost 2 on Windows ® to start 2 compute nodes. You can also run COMSOL with a distributed parametric sweep from the command line. See Running COMSOL in Parallel on Clusters for more information.
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Stationary for information about the continuation parametric solver versus parametric sweeps.
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