  Synaptic strength can be seen as probability to propagate impulse, and
according to synaptic plasticity, function could exist from propagation
activity to synaptic strength. If the function satisfies constraints such as
continuity and monotonicity, neural network under external stimulus will always
go to fixed point, and there could be one-to-one mapping between external
stimulus and synaptic strength at fixed point. In other words, neural network
"memorizes" external stimulus in its synapses. A biological classifier is
proposed to utilize this mapping.
