webppl/src/dists/delta.js

Probabilistic programming for the web

'use strict';
var ad = require('../ad');
var base = require('./base');
var types = require('../types');
var Delta = base.makeDistributionType({
    name: 'Delta',
    desc: 'Discrete distribution that assigns probability one to the single ' + 'element in its support. This is only useful in special circumstances as sampling ' + 'from ``Delta({v: val})`` can be replaced with ``val`` itself. Furthermore, a ``Delta`` ' + 'distribution parameterized by a random choice should not be used with MCMC based inference, ' + 'as doing so produces incorrect results.',
    params: [{
            name: 'v',
            desc: 'support element',
            type: types.any
        }],
    mixins: [base.finiteSupport],
    sample: function () {
        return ad.value(this.params.v);
    },
    score: function (val) {
        return ad.value(val) === ad.value(this.params.v) ? 0 : -Infinity;
    },
    support: function () {
        return [this.params.v];
    },
    base: function () {
        return this;
    },
    transform: function (x) {
        return this.params.v;
    }
});
module.exports = { Delta: Delta };