# User-adjustable parameters

The CTDE domain has several unique simulation parameters that can be edited in the System Properties window.

## The ODE solver

The CTDE domain provides several different mathematical methods for solving the ordinary differential equations (ODEs) used to simulate continuous or mixed-signal systems. (These methods are commonly called ODE solvers.) The ODE solver choice is user-selectable at execution time. Currently MLDesigner provides the six ODE solvers below.

Short name |
Long name |
Description |

DOPRI5 |
Dormand Prince |
A Dormand-Prince method with order 5(4), embedded error estimation, and variable step size control. |

DOPRI5D |
Dormand Prince Dense |
A Dormand-Prince method with order 5(4), embedded error estimation, variable step size control and dense output. |

FE |
Forward Euler |
One-step Euler-Cauchy Method |

RK2 |
Runge-Kutta 2 |
Second order Runge-Kutta method |

RK4 |
Runge-Kutta 4 |
Classical Runge-Kutta method of order 4 |

ROS4 |
Rosenbrock-Wanner 4 |
Rosenbrock-Wanner method of order 4 |

At the moment, the short name of the ODE solver has to be supplied as text to the **Solver** property.

## Solver parameters

Several parameters can be used to control the operation of the ODE solver. These parameters are listed below. (We assume that the reader is familiar with basic terms of ODE solvers shown in this table.)

Type |
Parameter |
Description |

float |
StepSize |
Initial step size of the ODE solver. For fixed-step solvers, this step size is used throughout the whole simulation. |

float |
MinStep |
Smallest allowed step size. If the error bounds cannot be met using this step size, the simulation is aborted. |

float |
MaxStep |
The largest allowed step size. MinStep and MaxStep are used only in variable-step solvers. |

int |
MaxNum |
Maximum number of iteration per step. This parameter applies only to implicit solvers. |

float |
RelTol |
Allowed relative local truncation error of the solver. This value is useful when the absolute value of different states differs significantly (that is, by several orders of magnitude). |

float |
AbsTol |
Maximum absolute local truncation error. Note that RelTol and AbsTol are used in conjunction if both values are non-zero. In this case, a weighted sum of these parameters is used as the maximum allowed local truncation error. |