BayesJS

A inference library for Bayesian Networks made with TypeScript.

Inferences

Currently there are three inferences algorithms:

• Junction tree algorithm
• Variable elimination
• Enumeration

Methods

infer(network: INetwork, nodes?: ICombinations, given?: ICombinations): number

Calculate the probability of a node's state.

This function receives a network, a node's state, and the knowing states and will return the probability of the node's state give.

As mentioned above, there are three inferences engines, by default the junction tree algorithm is used to execute the infer function.

It's important to remember that junction tree uses WeakMap to cache some internal results, if you are mutating the network or given object is advisable to shallow clone both objects before infer. Read more about JT cache here

import { infer, inferences } from 'bayesjs';

infer(network, nodes, give); // Junction tree algorithm

inferences.enumeration.infer(network, nodes, give);
inferences.variableElimination.infer(network, nodes, give);
inferences.junctionTree.infer(network, nodes, give);

Example

Given the rain-sprinkler-grasswet network. Image here.

import { infer } from 'bayesjs';

const network = // ...

// What is the probability that it is raining (RAIN = T)?
infer(network, { 'RAIN': 'T' }).toFixed(4) // 0.2000
// What is the probability that it is raining (RAIN = T), given the sprinkler is off (SPRINKLER = F)?
infer(network, { 'RAIN': 'T' }, { 'SPRINKLER': 'F' }).toFixed(4) // 0.2920

inferAll(network: INetwork, given?: ICombinations, options?: IInferAllOptions): INetworkResult)

Calculate all probabilities from a network by receiving the network, knowing states, and options. It returns an object with all results.

This method will execute the junction tree algorithm on each node's state.

Options

force

default: false

Enforces to clear junction tree cache before inferring all network. The junction tree uses WeakMap to store the cliques and potentials that are used at the algorithm.

• cliques weak stored by network
• potentials weak stored by cliques and given

This option is only necessary if you are mutation your network or given object instead of creating a new object before inferring each time.

precision

default: 8

Rounds the network results according to this value. To round the value we are using round-to.

Some rounds examples:

• 0.30000000000000004
  • 8 precision -> 0.3
  • 4 precision -> 0.3
  • 2 precision -> 0.3
• 0.3333333333333333
  • 8 precision -> 0.33333333
  • 4 precision -> 0.3333
  • 2 precision -> 0.33
• 0.9802979902088171
  • 8 precision -> 0.98029799
  • 4 precision -> 0.9803
  • 2 precision -> 0.98

Example

const network = {
  'Node 1': {
    id: 'Node 1',
    states: ['True', 'False'],
    parents: [],
    cpt: { True: 0.5, False: 0.5 },
  },
  'Node 2': {
    id: 'Node 2',
    states: ['True', 'False'],
    parents: [],
    cpt: { True: 0.5, False: 0.5 },
  },
  'Node 3': {
    id: 'Node 3',
    states: ['True', 'False'],
    parents: ['Node 2', 'Node 1'],
    cpt: [
      {
        when: { 'Node 2': 'True', 'Node 1': 'True' },
        then: { True: 0.5, False: 0.5 },
      },
      {
        when: { 'Node 2': 'False', 'Node 1': 'True' },
        then: { True: 0.5, False: 0.5 },
      },
      {
        when: { 'Node 2': 'True', 'Node 1': 'False' },
        then: { True: 0.5, False: 0.5 },
      },
      {
        when: { 'Node 2': 'False', 'Node 1': 'False' },
        then: { True: 0.5, False: 0.5 },
      },
    ],
  },
};

const given = { 'Node 1': 'True' }

inferAll(network, given)
// {
//   'Node 1': { True: 1, False: 0 },
//   'Node 2': { True: 0.5, False: 0.5 },
//   'Node 3': { True: 0.5, False: 0.5 },
// }

// Mutating the network...
network["Node 3"].cpt[0].then = { True: 0.95, False: 0.05 };

inferAll(network, given);
// Cached result - wrong
// {
//   'Node 1': { True: 1, False: 0 },
//   'Node 2': { True: 0.5, False: 0.5 },
//   'Node 3': { True: 0.5, False: 0.5 },
// }

inferAll(network, given, { force: true });
// {
//   'Node 1': { True: 1, False: 0 },
//   'Node 2': { True: 0.5, False: 0.5 },
//   'Node 3': { True: 0.725, False: 0.275 }
// }

addNode(network: INetwork, node: INode): INetwork

Add a node in a Bayesian Network.

This function receives a network and a node, check if the node can be appended on the network. If something is wrong an exception will be thrown, otherwise, a new network will return with the node added.

Example

import { addNode } from 'bayesjs';

const networkWithRainAndSprinkler = // ...

const grassWet = {
  id: 'GRASS_WET',
  states: [ 'T', 'F' ],
  parents: [ 'RAIN', 'SPRINKLER' ],
  cpt: [
    { when: { 'RAIN': 'T', 'SPRINKLER': 'T' }, then: { 'T': 0.99, 'F': 0.01 } },
    { when: { 'RAIN': 'T', 'SPRINKLER': 'F' }, then: { 'T': 0.8, 'F': 0.2 } },
    { when: { 'RAIN': 'F', 'SPRINKLER': 'T' }, then: { 'T': 0.9, 'F': 0.1 } },
    { when: { 'RAIN': 'F', 'SPRINKLER': 'F' }, then: { 'T': 0, 'F': 1 } }
  ]
};

const newtwork = addNode(networkWithRainAndSprinkler, grassWet);

License

MIT