public double eval(double i,double j){
  double evalKernel=Math.exp(-.5 * (Math.pow((i - j),2) / Math.pow(sigma,2)));
  return evalKernel;
}

public double eval ( double i , double j ) { double evalKernel = Math . exp ( - .5 * ( Math . pow ( ( i - j ) , 2 ) / Math . pow ( sigma , 2 ) ) ) ; return evalKernel ; }
evaluates the kernel at two given points
