  We prove that approximating the size of stopping and trapping sets in Tanner
graphs of linear block codes, and more restrictively, the class of low-density
parity-check (LDPC) codes, is NP-hard. The ramifications of our findings are
that methods used for estimating the height of the error-floor of moderate- and
long-length LDPC codes based on stopping and trapping set enumeration cannot
provide accurate worst-case performance predictions.
