public static double logpdf(double x, double mu, double sigma) {
    if(x <= 0.) {
      return Double.NEGATIVE_INFINITY;
    }
    final double xrel = (FastMath.log(x) - mu) / sigma;
    return MathUtil.LOG_ONE_BY_SQRTTWOPI - FastMath.log(sigma * x) - .5 * xrel * xrel;
  }
public static double logpdf ( double x , double mu , double sigma ) { if ( x <= 0. ) { return Double . NEGATIVE_INFINITY ; } final double xrel = ( FastMath . log ( x ) - mu ) / sigma ; return MathUtil . LOG_ONE_BY_SQRTTWOPI - FastMath . log ( sigma * x ) - .5 * xrel * xrel ; }
Probability density function of the normal distribution.

<pre>
1/(SQRT(2*pi)*sigma*x) * e^(-log(x-mu)^2/2sigma^2)
</pre>

@param x The value.
@param mu The mean.
@param sigma The standard deviation.
@return logPDF of the given normal distribution at x.