code: private void getOutput(double[] y) {
          if (y.length != outputLayer.units) {
              throw new IllegalArgumentException(String.format("Invalid output vector size: %d, expected: %d", y.length, outputLayer.units));
          }
          System.arraycopy(outputLayer.output, 0, y, 0, outputLayer.units);
      }
docs: Returns the output vector into the given array.
  @param y the output vector.