The Dittert conjecture, or Dittert–Hajek conjecture, is a mathematical hypothesis (in combinatorics) concerning the maximum achieved by a particular function of matrices with real, nonnegative entries satisfying a summation condition. The conjecture is due to Eric Dittert and (independently) Bruce Hajek. Let be a square matrix of order with nonnegative entries and with . Its permanent is defined as , where the sum extends over all elements of the symmetric group.