simple linear regression in javascript

lm.js

var _ = require('underscore');

function simple_linear_regression (x, y) {
    var sum_x = 0
        , sum_y = 0
        , sum_xy = 0
        , sum_xx = 0
        , cnt = 0
        , nrow = x.length
        , m = null
        , b = null;
    
    if ( x.length != y.length) {
        throw new Error('x and y must be vectors of the same length\n')
    }

    _.each(_.range(nrow), function (i) {
        sum_x += x[i]
        sum_y += y[i]
        sum_xx += Math.pow(x[i], 2) 
        sum_xy += x[i] * y[i]
    });

    m = (nrow*sum_xy - sum_x*sum_y) / (nrow*sum_xx - sum_x*sum_x);
    b = (sum_y/nrow) - (m*sum_x)/nrow;
    return [m, b]
}

x = [10.4,10.3,11.5,12.8,13.2,13.9]
y = [0.71,0.73,0.83,0.81,0.86,0.97]

fit = simple_linear_regression(x, y)

m = fit[0]
b = fit[1]

console.log(m) // 0.057002780623444764
console.log(b) // 0.13334991950827202