Exact Ground-State Energies of the Random-Field Ising Chain and Ladder
  We derive the exact ground-state energy of the one-dimensional Ising model in random fields taking values h, 0 and -h with general probabilities. The random-field Ising model on a ladder is also analyzed by showing its equivalence to the random-field Ising chain with field values h, -h and 0 for h<J. The zero-temperature transger matrix is used to obtain the results. 
Toshiyuki Hamasaki and Hidetoshi Nishimori