Solver Pane

The Solver pane includes parameters for selecting and configuring the solver for a model and for specifying the start and stop times for simulation. A solver computes the states of a dynamic system for each simulation time step over the specified time span for the simulation.

Once the model compiles, the Solver Information tooltip displays:

• The compiled solver name

• The compiled step size, typically specified by the Max step size parameter or the Fixed-step size (fundamental sample time) parameter.

Once the model compiles, the status bar displays the solver used for compiling and a carat (^) when:

• The software selects a different solver during compilation.

• You set the step size to auto or the solver determines a step size that is different from the specified value of the Max step size parameter or the Fixed-step size (fundamental sample time) parameter. The Solver Information tooltip displays the step size that the software determined.

When configuring the solver, consider that:

• Simulation time is not the same as clock time. For example, running a simulation for 10 seconds usually does not take 10 seconds. Total simulation time depends on factors such as model complexity, solver step sizes, and computer speed.

• Code generation requires selecting a fixed-step solver.

• Selecting a variable-step solver can significantly shorten the time required to simulate models in which states change rapidly or contain discontinuities.

The tables summarize the parameters available on the Solver pane of the Configuration Parameters dialog box.

Simulation Time

Parameter	Description
Start time	Simulation start time
Stop time	Simulation stop time

Solver Selection

Parameter	Description
Type	Choice of variable- or fixed-step solver
Solver	Solver that computes states and outputs for simulation

To see these parameters, click the arrow to expand the Solver Details section.

Variable-Step Solver Details

Parameter	Description
Max step size	Maximum step size to allow in simulations that use variable-step solvers
Min step size	Minimum step size for variable-step solver
Initial step size	Size of first step for variable-step solver
Relative tolerance	Relative tolerance for solver tolerance calculation
Absolute tolerance	Absolute tolerance for solver tolerance calculation
Auto scale absolute tolerance	Option to scale absolute tolerance based on state values
Shape preservation	Option to preserve shape of states using derivative information at each time step
Number of consecutive min steps	Number of steps less than or equal to minimum step size allowed before minimum step size violation occurs
Solver reset method	Option to specify whether solver recomputes Jacobian matrix during solver reset
Solver Jacobian Method	Method implicit solvers use to compute Jacobian matrix
Integration method	Integration for nonadaptive odeN variable-step solver
Maximum order	Order of numerical differentiation formulas used for ode15s solver
Daessc mode	Mode of operation for daessc solver
Continuous state refinement method	Method daessc solver uses to refine continuous state values

Variable-Step Zero-Crossing Detection

Parameter	Description
Zero-crossing control	Option to control how zero-crossing detection is enabled in the model
Algorithm	Choice of variable-step zero-crossing detection algorithm
Time tolerance	Definition of consecutive zero crossings
Signal threshold	State value at which adaptive zero-crossing algorithm can stop bracketing
Number of consecutive zero crossings	Threshold for issuing diagnostic due to consecutive zero crossings

Fixed-Step Solver Details

Parameter	Description
Fixed-step size (fundamental sample time)	Step size for fixed-step solver
Solver Jacobian Method	Method implicit solvers use to compute Jacobian matrix
Number of Newton's iterations	Number of Newton's method iterations used by ode14x and ode1be solvers
Extrapolation order	Extrapolation order for ode14x fixed-step solver

Fixed-Step Zero-Crossing Detection

Parameter	Description
Enable zero-crossing detection for fixed-step simulation	Option to use zero-crossing detection with fixed-step solver
Maximum number of bracketing iterations	Maximum number of iterations performed when locating zero crossing
Maximum number of zero-crossings per step	Maximum number of zero crossings to locate in a single time step

Tasking and Sample Time Options

Periodic sample time constraint	Option to specify constraints on model sample times
Sample time properties	Discrete sample time periods, offsets, and priorities
Treat each discrete rate as a separate task	Option to enable multitasking execution
Allow tasks to execute concurrently on target	Option to enable concurrent tasking behavior for model
Automatically handle rate transition for data transfer	Option to ensure integrity of data transfer between different sample times in deployed code
Deterministic data transfer	Deterministic data transfer behavior for automatically inserted Rate Transition blocks
Allow multiple tasks to access inputs and outputs	Option to treat root-level input and output ports as part of each connected task in rate-based model
Higher priority value indicates higher task priority	Priority ordering for real-time system targets

These configuration parameters are in the Advanced parameters section.

Parameter	Description
Enable decoupled continuous integration	Option to speed up simulation by decoupling continuous state integration from discrete sample times
Enable minimal zero-crossing impact integration	Option to reduce the effect of zero crossings on continuous state integration