Graphology ForceAtlas2

JavaScript implementation of the ForceAtlas2 algorithm for graphology.

Reference

Jacomy M, Venturini T, Heymann S, Bastian M (2014) ForceAtlas2, a Continuous Graph Layout Algorithm for Handy Network Visualization Designed for the Gephi Software. PLoS ONE 9(6): e98679. https://doi.org/10.1371/journal.pone.0098679

Installation

npm install graphology-layout-forceatlas2

Usage

• Pre-requisite
• Settings
• Synchronous layout
• Webworker
• #.inferSettings

Pre-requisites

Each node's starting position must be set before running ForceAtlas 2 layout. Two attributes called x and y must therefore be defined for all the graph nodes. graphology-layout can be used to initialize these attributes to a random or circular layout, if needed.

Note also that the algorithm has an edge-case where the layout cannot be computed if all of your nodes starts with x=0 and y=0.

Settings

• adjustSizes ?boolean [false]: should the node's sizes be taken into account?
• barnesHutOptimize ?boolean [false]: whether to use the Barnes-Hut approximation to compute repulsion in O(n*log(n)) rather than default O(n^2), n being the number of nodes.
• barnesHutTheta ?number [0.5]: Barnes-Hut approximation theta parameter.
• edgeWeightInfluence ?number [1]: influence of the edge's weights on the layout. To consider edge weight, don't forget to pass weighted as true when applying the synchronous layout or when instantiating the worker.
• gravity ?number [1]: strength of the layout's gravity.
• linLogMode ?boolean [false]: whether to use Noack's LinLog model.
• outboundAttractionDistribution ?boolean [false]
• scalingRatio ?number [1]
• slowDown ?number [1]
• strongGravityMode ?boolean [false]

Synchronous layout

import forceAtlas2 from 'graphology-layout-forceatlas2';

const positions = forceAtlas2(graph, {iterations: 50});

// With settings:
const positions = forceAtlas2(graph, {
  iterations: 50,
  settings: {
    gravity: 10
  }
});

// To directly assign the positions to the nodes:
forceAtlas2.assign(graph);

Arguments

• graph Graph: target graph.
• options object: options:
  • iterations number: number of iterations to perform.
  • attributes ?object: an object containing custom attribute name mapping:
    • weight ?string [weight]: name of the edge weight attribute.
  • weighted ?boolean [false]: whether to consider edge weight.
  • settings ?object: the layout's settings (see #settings).

Webworker

If you need to run the layout's computation in a web worker, the library comes with a utility to do so:

Example

import FA2Layout from 'graphology-layout-forceatlas2/worker';

// The parameters are the same as for the synchronous version, minus `iterations` of course
const layout = new FA2Layout(graph, {settings: {gravity: 1}, weighted: true});

// To start the layout
layout.start();

// To stop the layout
layout.stop();

// To kill the layout and release attached memory
layout.kill();

// Assess whether the layout is currently running
layout.isRunning();

WARNING!: if you are using webpack to bundle your code, avoid the cheap-eval-like options for the devtool setting. Some users noticed that it interacts in mysterious ways with the library's code and cause performance to drop dramatically when using the worker. Note that this should have been fixed from v0.5.0.

#.inferSettings

If you don't know how to tune the layout's settings and want to infer them from your graph, you can use the #.inferSettings method:

import forceAtlas2 from 'graphology-layout-forceatlas2';

const sensibleSettings = forceAtlas2.inferSettings(graph);
const positions = forceAtlas2(graph, {
  iterations: 50,
  settings: sensibleSettings
});

// Alternatively using the graph's order instead of a graph instance
const sensibleSettings = forceAtlas2.inferSettings(500);