It is speculated that the most probable channel noise realizations (instantons) that cause the iterative decoding of low-density parity-check codes to fail make the decoding not to converge. The Wibergs formula is generalized for the case when the part of a computational tree that contributes to the output at its center is ambiguous. Two methods of finding the instantons for large number of iterations are presented and tested on Tanners [155, 64, 20] code and Gaussian channel. The inherently dynamic instanton with effective distance of 11.475333 is found.
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