code: public static double sinusProduct(int start, int end, double[] alpha) {
      double result = 1;
      for(int j = start; j < end; j++) {
        result *= FastMath.sin(alpha[j]);
      }
      return result;
    }
docs: Computes the product of all sinus values of the specified angles from start
  to end index.
  
  @param start the index to start
  @param end the index to end
  @param alpha the array of angles
  @return the product of all sinus values of the specified angles from start
  to end index