In early SMT systems, such as (Koehn, 2004), changes in word order when a sentence is translated were modeled by means of a penalty that is in-curred when the decoder chooses, as the next source phrase to be translated, a phrase that does not immediately follow the previously translated source sentence.
the system penalizes deviations from monotone order, with the magnitude of the penalty being proportional to distance in the source sentence between the end of the previously translated source phrase and the start of the newly chosen source phrase.