'Returns the derivative of the logistic (sigmoid) function at y (output)
Args:
y (Tensor or OpTree): input. y = f(x)
Returns:
OpTree: Derivative of the Logistic (sigmoid)
Returns 1 if shortcut is True.
Returns derivative (y*(1-y)) if shortcut is False.'

def bprop(self, y):

    return self.bprop_func(y)
