  In order to understand the performance of a code under maximum-likelihood
(ML) decoding, one studies the codewords, in particular the minimal codewords,
and their Hamming weights. In the context of linear programming (LP) decoding,
one's attention needs to be shifted to the pseudo-codewords, in particular to
the minimal pseudo-codewords, and their pseudo-weights. In this paper we
investigate some families of codes that have good properties under LP decoding,
namely certain families of low-density parity-check (LDPC) codes that are
derived from projective and Euclidean planes: we study the structure of their
minimal pseudo-codewords and give lower bounds on their pseudo-weight.
