w-distributions/src/uniform.mjs

merge to `w-statistic`

async function wUniformDistribution(a, b) {

    function UniformDistribution(a, b) {
        if (!(this instanceof UniformDistribution)) {
            return new UniformDistribution(a, b)
        }

        if (typeof a !== 'number' && a !== undefined) {
            throw TypeError('mean must be a number')
        }
        if (typeof b !== 'number' && b !== undefined) {
            throw TypeError('sd must be a number')
        }

        this._a = typeof a === 'number' ? a : 0
        this._b = typeof b === 'number' ? b : 1

        if (this._b <= this._a) {
            throw new RangeError('a must be greater than b')
        }

        this._k = 1 / (this._b - this._a)
        this._mean = (this._a + this._b) / 2
        this._var = (this._a - this._b) * (this._a - this._b) / 12
    }

    UniformDistribution.prototype.pdf = function (x) {
        return (x < this._a || x > this._b) ? 0 : this._k
    }

    UniformDistribution.prototype.cdf = function (x) {
        if (x < this._a) return 0
        else if (x > this._b) return 1
        else return (x - this._a) * this._k
    }

    UniformDistribution.prototype.inv = function (p) {
        if (p < 0 || p > 1) return NaN
        else return p * (this._b - this._a) + this._a
    }

    UniformDistribution.prototype.median = function () {
        return this._mean
    }

    UniformDistribution.prototype.mean = function () {
        return this._mean
    }

    UniformDistribution.prototype.variance = function () {
        return this._var
    }

    return UniformDistribution(a, b)
}

export default wUniformDistribution