code: public void setWeightDecay(double weightDecay)
      {
          if(weightDecay < 0 || weightDecay >= 1 || Double.isNaN(weightDecay))
              throw new ArithmeticException("Weight decay must be in [0,1), not " + weightDecay);
          this.weightDecay = weightDecay;
      }
docs: Sets the weight decay used for each update. The weight decay must be in
  the range [0, 1). Weight decay values must often be very small, often
  1e-8 or less.
  
  @param weightDecay the weight decay to apply when training