PhaPl web application for automatic building and research of phase portraits on plane

The article aims to document PhaPl that’s a teaching web application to plot and research phase portraits of autonomous systems of 2 differential equations on a plane. The web application is very different compared with previously known programs: it has very easy graphical user interface and it gives clarity because it demonstrates all steps of solution. To get the full solution, it is enough to just enter a system to research. Initial conditions to plot phase trajectories are chosen automatically. Graphical representation of the phase plane is interactive. The web application is based on popular Free Software (SymPy, PyPy.js, MathJax, LZMA-JS). The web application is portable and works in web browsers that support JavaScript and canvas element of HTML5. The web application can be downloaded and used offline without connection to the Internet. The article describes advantages, disadvantages and peculiar properties of the web application. The software is deployed in Plekhanov Russian University of Economics since 2018.