docs: function dnorm(mu, sigma, logp) {
        var c;
  
        logp = logp === true;
        c = Math.log(twopi);
        return function(x) {
           var z, p;
  
           if (utils.hasNaN(x, mu, sigma)) { return NaN; }
           if (utils.isInfinite(sigma)) {
              return logp ? -Infinity : 0;
           }
           if (utils.isInfinite(x) && mu === x) { return NaN; }
           if (sigma < 0) { return NaN; }
           if (sigma === 0) { return x === mu ? Infinity : logp ? -Infinity : 0; }
  
           z = (x - mu) / sigma;
           p = -0.5 * (c + z * z) - Math.log(sigma);
           return logp ? p : Math.exp(p);
        };
     }