Unformatted text preview: must be made “(a) use of and (b) open (or, for that matter, circuits.” (Fredkin
Any output of generalpurpose signalprocessing primitive) in wire, and sirnilarly any input of a gate only to
& a gate 1982)
meant to be aTo↵oli,can be connected only to the input of a order to obtain adequate computing power.
the output of a wire. The interpretation of such a circuit in terms of conventional sequential computation is
iSuppose, for instance, that one desiresof an "instantaneous" combinational element invertible. In Figure 4b
mmediate, as the gate plays the role to compute the AND function, which is not and the wire that of a
oelay inputs u aembeddedfed an interconnection line.and b, closed x2onservativelogic circuit, value 0. In and
d nly element nd x1 are in with arbitrary values a In a while c is fed with the constant all inputs this
case, the any elements are connected within the circuit (Figure 3a). Such a circuit corresponds to what ill
outputs ofy1 output will provide the desired value ab ("a AND b"), while the other two outputs v and y2 win
yield the called a a closed (or i and ¬ ) . Thus, An open c the AND function can possesses by means of
physics is"unrequested" values asolatedabsystem. intuitively,onservativelogic circuitbe realized a number of
the Fredkin gate asoutput ports is willing to supply "constants"ato this gate alongside withof asargument, and
external input and long as one (Figure 3b). In isolation, such circuit might be thought the a transducer
(accept "garbage" from it which, depending on its initial situation is respond with in particular Output
typically, with memory) alongside with the result. This state, will so common a computation with
iequence to any particular it will sequence. However, usually such aterminology be thought of as awith it in a
s nvertible primitives that input be convenient to introduce some circuit will in order to deal portion of
p larger circuit; thence the notation for input and output ports...
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 Fall '13
 BruceMacLennan
 Logic gate, fredkin gate, Fredkin

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