This function supposes that upon loading a network, its structure is already
known, and writes
only the weights and biases (i.e. the variable parts) of the network in ASCII
format. No checking is done.
NOTE
This function was created because for large networks the size of the network
save file may become excessively large. If the network's structure is fixed,
there is no need to store it.
Also note, that no structure information or history values (see HIST-flags)
are stored! Use this function only if the network's structure is easily
recreated, e.g. using create_ff_net or create_sharednet.
