code: function dlnorm(meanlog, sdlog, logp) {
        logp = logp === true;
  
        if (utils.hasNaN(meanlog, sdlog) || sdlog < 0) {
           return function() { return NaN; };
        }
  
        return function(x) {
           var z;
  
           if (utils.hasNaN(x)) { return NaN; }
           if (sdlog === 0) {
              return Math.log(x) === meanlog ? Infinity
                                      : logp ? -Infinity
                                             : 0;
           }
           if (x <= 0) { return logp ? -Infinity : 0; }
  
           z = (Math.log(x) - meanlog) / sdlog;
           return logp ? -(logRoot2pi + 0.5 * z * z + Math.log(x * sdlog))
                       : recipRoot2pi * Math.exp(-0.5 * z * z) / (x * sdlog);
        };
     }
docs: Evaluates the lognormal distribution's density function at `x`.
  
  Expects $x > 0$ and $\textrm{sdlog} > 0$.
  @fullName dlnorm(meanlog, sdlog, logp)(x)
  @memberof lognormal