Close-packed dimers on nonorientable surfaces

Abstract The problem of enumerating dimers on an M × N net embedded on nonorientable surfaces is considered. We solve both the Mobius strip and Klein bottle problems for all  M and  N with the aid of imaginary dimer weights. The use of imaginary weights simplifies the analysis, and as a result we obtain new compact solutions in the form of double products. The compact expressions also permit us to establish a general reciprocity theorem.