public NormalDistributionFunction2D(double mean,double std){
  if (std <= 0) {
    throw new IllegalArgumentException("Requires 'std' > 0.");
  }
  this.mean=mean;
  this.std=std;
  this.factor=1 / (std * Math.sqrt(2.0 * Math.PI));
  this.denominator=2 * std * std;
}

public NormalDistributionFunction2D ( double mean , double std ) { if ( std <= 0 ) { throw new IllegalArgumentException ( "Requires 'std' > 0." ) ; } this . mean = mean ; this . std = std ; this . factor = 1 / ( std * Math . sqrt ( 2.0 * Math . PI ) ) ; this . denominator = 2 * std * std ; }
constructs a new normal distribution function .
