tokens: When each layer is handled by the piecewise linear activation function , e.g. , using the rectified linear unit ( ReLU ) function or its variants , such as the parametric ReLU and leaky ReLU function , to a certain extent , the interpolated network can maintain the characteristic of linearity for the output of each layer , which finally leads to continuous intermediate - effect images created by the new interpolated networks when continuously varying the trade - off parameter .