webppl/src/dists/uniform.js

Probabilistic programming for the web

'use strict';
var ad = require('../ad');
var base = require('./base');
var types = require('../types');
var util = require('../util');
var Uniform = base.makeDistributionType({
    name: 'Uniform',
    desc: 'Continuous uniform distribution over ``[a, b]``',
    params: [
        {
            name: 'a',
            desc: 'lower bound',
            type: types.unboundedReal
        },
        {
            name: 'b',
            desc: 'upper bound (>a)',
            type: types.unboundedReal
        }
    ],
    wikipedia: 'Uniform_distribution_(continuous)',
    mixins: [base.continuousSupport],
    sample: function () {
        var u = util.random();
        return (1 - u) * ad.value(this.params.a) + u * ad.value(this.params.b);
    },
    score: function (val) {
        if (ad.scalar.lt(val, this.params.a) || ad.scalar.gt(val, this.params.b)) {
            return ad.scalar.neg(Infinity);
        }
        return ad.scalar.neg(ad.scalar.log(ad.scalar.sub(this.params.b, this.params.a)));
    },
    support: function () {
        return {
            lower: this.params.a,
            upper: this.params.b
        };
    }
});
module.exports = { Uniform: Uniform };