Sims.jl

A Julia package for equation-based modeling and simulations using ModelingToolkit.

Background

Sims is like a lite version of Modelica. This package is for non-causal modeling in Julia. The idea behind non-causal modeling is that the user develops models based on components which are described by a set of equations. A tool can then transform the equations and solve the differential algebraic equations. Non-causal models tend to match their physical counterparts in terms of their specification and implementation.

Causal modeling is where all signals have an input and an output, and the flow of information is clear. Simulink is the highest-profile example. The problem with causal modeling is that it is difficult to build up models from components.

The highest profile noncausal modeling tools are in the Modelica family. The MathWorks company also has Simscape that uses Matlab notation. Modelica is an object-oriented, open language with multiple implementations. It is a large, complex, powerful language with an extensive standard library of components.

This implementation follows the work of David Broman (thesis and code) and George Giorgidze (Hydra code and thesis) and Henrik Nilsson and their functional hybrid modeling. Sims is most similar to Modelyze by David Broman (report).

Sims creates a ModelingToolkit component. ModelingToolkit can be used directly for noncausal modeling with more traditional composition of components with connect and subsystems. Sims differs by using a more functional approach to composition.

Installation

Sims is an installable package. To install Sims, use the following:

Pkg.add("Sims")

Sims.jl has one main module named Sims and the following submodules:

• Sims.Lib – the standard library

• Sims.Examples – example models, including:

• Sims.Examples.Basics
• Sims.Examples.Lib