protected static double calcSigmaFromMu(double mu){
  double sigma=Math.sqrt(mu);
  if (sigma < 0.5) {
    sigma=0.5;
  }
  return sigma;
}

protected static double calcSigmaFromMu ( double mu ) { double sigma = Math . sqrt ( mu ) ; if ( sigma < 0.5 ) { sigma = 0.5 ; } return sigma ; }
calculate the standard deviation ( sigma ) . note that for poisson distributions the variance is equal to expected value ( mu ) .
