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Use local solver when referencing model

Option to use local solver to solve referenced model as separate system of equations

Since R2022a

Model Configuration Pane: Model Referencing

Description

The Use local solver when referencing model configuration parameter specifies how the software solves the system implemented by a referenced model. When you select this parameter, the software solves the referenced model as a separate set of differential equations using the solver that the current referenced model specifies for the Solver configuration parameter.

While the top solver can be a fixed-step or variable-step solver, the local solver must be a fixed-step solver. Specify the fixed step size for the local solver using the Fixed-step size (fundamental sample time) configuration parameter of the referenced model.

Using a local solver can facilitate system composition and integration. When you use local solvers, you can solve referenced models in system-level simulations using the same solver and step size used to design and test each model in isolation. Using local solvers can also reduce the amount of configuration adjustments you need to make to configuration parameters in referenced models while integrating the model into a larger system.

For some systems, using a local solver can improve simulation performance by allowing you to choose a solver that is more appropriate to solve the system in the referenced model or by reducing the number of redundant calculations in systems that have a wide range of dynamics among components.

For an example, see Improve Simulation Performance by Using Local Solvers.

For more information about local solvers, see Use Local Solvers in Referenced Models.

Set Configuration Parameter for Referenced Model

In a model reference hierarchy, how you open the Configuration Parameters dialog box determines whether you edit the configuration parameter for the top model in the current model hierarchy or the current referenced model.

  • Top model in the current model hierarchy — In the Simulink® Toolstrip, on the Modeling tab, click Model Settings.

  • Current referenced model — In the Simulink Toolstrip, on the Modeling tab, click the Model Settings button arrow. Then, in the Referenced Model section, select Model Settings.

Alternatively, open the referenced model as a top model. Then, in the Simulink Toolstrip, on the Modeling tab, click Model Settings.

Settings

off (default) | on
on

The software uses a local solver to solve the referenced model as a separate set of differential equations. Specify the local solver using the Solver configuration parameter of the referenced model.

off

The software solves the referenced model as part of the parent system using the parent solver.

Examples

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Open the model SecondOrderSystemTop. The model contains a Ramp block that provides the input signal for a Model block that references a model of a second-order system. The Model block output signal connects to an Outport block.

topmdl = "SecondOrderSystemTop";
open_system(topmdl)

The model SecondOrderSystemTop.

To navigate inside the referenced model, double-click the Model block. Alternatively, create a Simulink.BlockPath object for the Model block and use the open function to open the referenced model in the context of the model hierarchy.

mdlblkpath = Simulink.BlockPath(topmdl + "/Model");
open(mdlblkpath)

The contents of the model reference.

The referenced model implements the second-order system using a Transfer Fcn block and contains a Step block that models a change or disturbance to the system.

The system transfer function is specified in the Transfer Fcn block using two model workspace variables, wn and z, which represent the natural frequency of the system, in radians per second, and the system damping coefficient.

Configure the system with a natural frequency of 100 radians per second by specifying the value of the variable wn as 100 in the model workspace.

refmdl = "SecondOrderSystem";
mdlwksp = get_param(refmdl,"ModelWorkspace");
assignin(mdlwksp,"wn",100)

Configure the referenced model to use a local solver with a step size of 0.01 seconds. You can configure the settings for the referenced model from the top model using the Property Inspector or the Block Parameters dialog box.

  1. Open the Property Inspector. On the Modeling tab, expand the Design section and select Property Inspector, or press Ctrl+Shift+I.

  2. To open the Configuration Parameters dialog box for the referenced model, select the Model block. Then, in the Property Inspector, expand the Solver section and click the hyperlink next to the Use local solver parameter.

  3. Configure the model to use a local solver when referenced in a model hierarchy. In the Configuration Parameters dialog box, on the Model Referencing pane, select Use local solver when referencing model.

  4. Select the fixed-step ode3 as the local solver. On the Solver pane, from the Type list, select Fixed-step. Then, from the Solver list, select ode3 (Bogacki-Shampine).

  5. Set the local solver step size to 0.01 seconds. On the Solver pane, expand Solver details. Then, in the Fixed-step size (fundamental sample time) box, enter 0.01.

  6. Click OK.

Alternatively, use the set_param function to configure the parameters.

set_param(refmdl,UseModelRefSolver="on",...
    SolverType="Fixed-Step",Solver="ode3",FixedStep="0.01")

In the top model, the Model block indicates the local solver you specify.

The solver name ode3 is on the bottom of the Model block icon.

Specify the communication step size for the model reference. The communication step size specifies when the parent and local solvers exchange data and is registered as a discrete sample time in the top model.

The Ramp block in the top model has a slope of 0.2, and the top solver uses a step size of 0.2 seconds. Because the input signal from the top model changes slowly compared to the dynamics of the second-order system, the communication step size can be much larger than the local solver step size without significant effect on the accuracy of the simulation results.

Specify the communication step size as 0.4 seconds. Select the Model block. Then, in the Property Inspector, under Solver, in the Communication step size box, enter 0.4.

Alternatively, use the set_param function to set the CommunicationStepSize parameter.

set_param(topmdl + "/Model",CommunicationStepSize="0.4")

Simulate the model, using the local solver to compute the response of the second-order system.

out = sim(topmdl);

To view the simulation results, open the Simulation Data Inspector. On the Simulation tab, under Review Results, click Data Inspector. Alternatively, call the Simulink.sdi.view function.

Simulink.sdi.view

Plot the signals named System Response and System Response - Top on separate subplots. Alternatively, use the Simulink.sdi.loadView function to load the view named FastSecondOrderSystem, which was created for this example.

Simulink.sdi.loadView("FastSecondOrderSystem.mldatx");

Two subplots in the Simulation Data Inspector display the system response. The top plot shows the system response logged inside the referenced model, and the bottom plot shows the system response logged from the top model.

The System Response and System Response - Top signals are the same signal, logged in different locations. The System Response signal is logged inside the referenced model at a rate determined by the local solver step size. The System Response - Top signal is logged by the Outport block in the top model at a rate determined by the top solver step size. Because the local solver step size is much smaller than the top solver step size, the System Response signal captures the system response to the change in the input signal when the Step block output value changes with higher fidelity.

In the System Response signal, you can see the effect of the local solver interpolating the input signal with a zero-order hold between each communication step. If you zoom on the time axis around 5 seconds, you can see the oscillations in the system response to the step.

A subplot in the Simulation Data Inspector shows the signal named System Response between simulation times of approximately 3 seconds and 7 seconds.

Open the model SecondOrderSystemTop. The model contains a Ramp block that provides the input signal for a Model block that references a model of a second-order system. The Model block output signal connects to an Outport block.

topmdl = "SecondOrderSystemTop";
open_system(topmdl)

The model SecondOrderSystemTop.

To navigate inside the referenced model, double-click the Model block. Alternatively, create a Simulink.BlockPath object for the Model block and use the open function to open the referenced model in the context of the model hierarchy.

mdlblkpath = Simulink.BlockPath(topmdl + "/Model");
open(mdlblkpath)

The contents of the model reference.

The referenced model implements the second-order system using a Transfer Fcn block and contains a Step block that models a change or disturbance to the system.

The system transfer function is specified in the Transfer Fcn block using two model workspace variables, wn and z, which represent the natural frequency of the system, in radians per second, and the system damping coefficient.

Configure the system with a natural frequency of 1 radian per second by specifying the value of the variable wn as 1 in the model workspace.

refmdl = "SecondOrderSystem";
mdlwksp = get_param(refmdl,"ModelWorkspace");
assignin(mdlwksp,"wn",1)

Configure the referenced model to use a local solver with a step size of 0.4 seconds. You can configure the settings for the referenced model from the top model using the Property Inspector or the Block Parameters dialog box.

  1. Open the Property Inspector. On the Modeling tab, expand the Design section and select Property Inspector, or press Ctrl+Shift+I.

  2. To open the Configuration Parameters dialog box for the referenced model, select the Model block. Then, in the Property Inspector, expand the Solver section and click the hyperlink next to the Use local solver parameter.

  3. Configure the model to use a local solver when referenced in a model hierarchy. In the Configuration Parameters dialog box, on the Model Referencing pane, select Use local solver when referencing model.

  4. Select the fixed-step ode3 as the local solver. On the Solver pane, from the Type list, select Fixed-step. Then, from the Solver list, select ode3 (Bogacki-Shampine).

  5. Set the local solver step size to 0.4 seconds. On the Solver pane, expand Solver details. Then, in the Fixed-step size (fundamental sample time) box, enter 0.4.

  6. Click OK.

Alternatively, use the set_param function to configure the parameters.

set_param(refmdl,UseModelRefSolver="on",...
    SolverType="Fixed-Step",Solver="ode3",FixedStep="0.4")

In the top model, the Model block indicates the local solver you specify.

The solver name ode3 is on the bottom of the Model block icon.

When the local solver step size is larger than the parent solver step size, inherit the communication step size by specifying the Communication step size parameter as -1. The communication step size specifies when the parent solver and local solver exchange data and is registered as a discrete sample time in the parent model.

set_param(topmdl + "/Model",CommunicationStepSize="-1")

Simulate the model, using the local solver to compute the response of the second-order system.

out = sim(topmdl,StopTime="20");

To view the simulation results, open the Simulation Data Inspector. On the Simulation tab, under Review Results, click Data Inspector. Alternatively, call the Simulink.sdi.view function.

Simulink.sdi.view

Plot the signals named System Response and System Response - Top on separate subplots. Alternatively, use the Simulink.sdi.loadView function to load the view named SlowSecondOrderSystem, which was created for this example.

Simulink.sdi.loadView("SlowSecondOrderSystem.mldatx");

Two subplots in the Simulation Data Inspector display the system response. The top plot shows the system response logged inside the referenced model, and the bottom plot shows the system response logged from the top model.

The System Response and System Response - Top signals are the same signal, logged in different locations. The System Response signal is logged inside the referenced model at a rate determined by the local solver step size. The System Response - Top signal is logged by the Outport block in the top model at a rate determined by the top solver step size. Fewer data points are logged for the System Response signal because the local solver step size is larger than the parent solver step size.

Tips

  • You can use Model block parameters to specify:

    • The communication step size, which specifies the rate at which the local and parent solvers exchange data

    • How the local solver extrapolates inputs from the parent solver

    • How the local solver interpolates state or output values to provide output signal values to the parent solver

  • Before R2024a: When the top solver is a fixed-step solver, the step size for the local solver must be an integer multiple of the parent solver step size.

Recommended Settings

ApplicationSetting
Debuggingoff
TraceabilityNo impact
EfficiencyNo recommendation
Safety precautionNo impact

Programmatic Use

Parameter: UseModelRefSolver
Value: "on" | "off"
Default: "off"

Version History

Introduced in R2022a

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