# An Overview of package pysd2r

# Introduction

The goal of this package is to allow R users run system dynamics models using the pysd, developed by James Houghton. The pysd project “is a simple library for running System Dynamics models in python, with the purpose of improving integration of Big Data and Machine Learning into the SD workflow.”

pysd2r has been tested with python3, and the following command was used to install pysd from source.

Source link:

python3 setup.py install

Given R’s facility for also providing big data and machine learning support, this package opens up the functionality of pysd for R users, and provides an interface to the basic set of methods provided by pysd, including the functions:

- pysd.read_vensim()
- model.run()

The API provide by pysd2r includes the following functions (for list of parameters type ?function_name in R) which call the mapping functions in pysd.

- get_python_info() - Returns the python version currently used by reticulate
- pysd_connect() - Creates an object to facilitate interaction with pysd
- read_vensim() - Loads a Vensim simulation file (mdl)
- read_xmile() - Loads a XMILE simulation file (.xmile)
- run_model() - Runs a simulation model
- set_components() - Changes a model parameter
- get_timestep() - Gets the time step (DT) from the model
- get_initial_time() - Gets the initial time from the model
- get_final_time() - Gets the final time from the model
- set_time_values() - Sets the initial time, final time, and timestep
- print() - Implementation of generic print function of ipysd S3 object
- get_doc() - Gets the model variables and returns as a tibble
- reload_model() - Reloads the original mdl file

The following example shows how pysd2r can be used to run a simulation model (Population.mdl which is a one-stock model of population growth)

    library(pysd2r)  # load pysd2r
    library(ggplot2) # load ggplot2
    library(tibble)  # load tibble

First, a connection is made to pysd

    py <- pysd_connect()

Next, the vensim file is opened.

    target <- system.file("models/vensim", "Population.mdl", package = "pysd2r")
    py <- read_vensim(py, target)

The returning object (ipysd, and S3 class) can be inspected. This is a list with two elements. The first is the reference to pysd, the second is a referece to the translated python model

    str(py)

With this reference, the simulation can be run by calling the run_model() function.

    results <- run_model(py)

The results from the tibble can be shown.

    results

These results can also be processed using ggplot2.

    ggplot(data=results)+
      geom_point(aes(x=TIME,y=Population),colour="blue")