It is important to note that when a variable node is fixed to a specific value, the decoder is now sampling possible solutions with that fixed bit, which is different from the ML and MAP problems above. Furthermore, if there is a unique solution and a bit is fixed which does not match the solution, the decoder will fail instead of correcting that bit. For example, fixing the most reliable bit in guided decimation may mean fixing a bit which is still far from reliable and could go either way. On the other hand, fixing a bit could help the decoder converge faster and also break out of trapping sets. In this sense, decimation can be very helpful decoding degenerate stabilizer codes where there are many valid solutions and BP has a difficult time picking one to converge to.
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