title	PathView: A Graphical User Interface for System Simulation
tags	Python block diagram system modelling
authors	name orcid corresponding affiliation Remi Delaporte-Mathurin 0000-0003-1064-8882 true 1 name affiliation Tasnim Zulfiqar 1 name orcid affiliation James Dark 0000-0002-0456-7210 1
affiliations	name index ror Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, 02139, USA 1 042nb2s44
date	12 August 2025
bibliography	paper.bib

Summary

PathView is an interactive, browser-based graphical interface for the system simulation framework PathSim [@Rother2025]. It enables users to build models quickly in an intuitive, visual environment. Built with ReactFlow [@reactflow], PathView allows users to:

• Drag and drop simulation nodes onto a canvas.
• Connect nodes to define system structure.
• Create and manage subsystems for hierarchical modelling.
• Configure event detection and advanced simulation options.
• Configure solver parameters
• Easily extend functionality through a modular architecture.

In addition to mirroring nearly all of PathSim's capabilities, PathView uses Jinja2 [@jinja] templates to generate fully executable Python scripts from graphical models, enabling seamless transition between GUI-based and code-based workflows.

Statement of need

PathSim is a powerful and flexible simulation framework for modelling complex systems. However, building large-scale or intricate models solely through Python scripting can be cumbersome and error-prone, particularly for new users or for projects that benefit from visual inspection of system layout. This is for example the case for nuclear fusion fuel cycle applications [@meschini_modeling_2023; @meschini_impact_2025]. Many established simulation platforms, such as MathWorks Simulink [@simulink] or Aspen Plus [@aspen], provide graphical user interfaces to enhance usability, model comprehension, and collaboration. Until now, such a visual modelling environment was missing for PathSim. PathView fills this gap by providing a modern, interactive, and extensible GUI, reducing the barrier to entry for new users and improving productivity for experienced modellers.

Examples

PathView includes several pre-built example graphs in the example_graphs directory that demonstrate different functionalities:

• harmonic_oscillator.json - Simple oscillator simulation (see \autoref{fig:example} and \autoref{fig:example_results})
• pid.json - PID controller example
• linear_feedback.json - Linear feedback system
• pendulum.json - Pendulum example
• spectrum.json - Spectral analysis example
• bouncing_ball.json - Example showcasing event detection
• thermostat.json - Thermostat demo with event detection
• stick_slip.json - Example showcasing the use of the Switch block

{ width=100% }

{ width=100% }

We also provide an example demonstrating the integration of external tools infestim_two_walls.json: a two-wall hydrogen diffusion model integrating the FESTIM hydrogen tranport code [@delaporte-mathurin_festim_2024].

Features

• Node creation and connection: Choose from 60+ different simulation node types, configure parameters, and connect them visually.
• Integrated simulation: Run PathSim simulations directly from the GUI.
• Interactive visualisation: Embedded plotly plots for interactive data exploration. Export results data to CSV or export graph to HTML.
• Advanced global variables: Define global variables, including via an integrated Python editor for complex expressions.
• Flexible I/O: Save and load models in JSON format; export to Python scripts for advanced or automated use.
• Modular and extensible: Designed for easy integration of new node types and custom functionality.
• Custom styling: Change node colours for improved readability.

References