  Four different ways of obtaining low-density parity-check codes from expander
graphs are considered. For each case, lower bounds on the minimum stopping set
size and the minimum pseudocodeword weight of expander (LDPC) codes are
derived. These bounds are compared with the known eigenvalue-based lower bounds
on the minimum distance of expander codes. Furthermore, Tanner's
parity-oriented eigenvalue lower bound on the minimum distance is generalized
to yield a new lower bound on the minimum pseudocodeword weight. These bounds
are useful in predicting the performance of LDPC codes under graph-based
iterative decoding and linear programming decoding.
