摘 要: |
It is shown that the relativistic invariance is very important in the study of integrable systems. Using the relativistic invariant sine-Gordon equation, the Tzitzeica equation, the Toda fields and the second heavenly equation as dual relations, some continuous and discrete integrable positive hierarchies such as the potential modified Korteweg-de Vries hierarchy, the potential Fordy-Gibbons hierarchies, the (2+1)-dimensional potential dispersionless Kadomtsev-Petviashvili like (dKPL) hierarchy, the differential-difference dKPL hierarchy and the heavenly hierarchies are changed to the integrable negative hierarchies including the sG hierarchy and the Tzitzeica hierarchy, the continuous Toda hierarchy, the differential-difference Toda hierarchies and negative heavenly hierarchy. In (1+1)-dimensional cases the positive/negative hierarchy dualities are guaranteed by the dualities between the recursion operators and their inverse operators. In (2+1)-dimensional cases, the positive/negative hierarchy dualities are explicitly shown by using the formal series symmetry approach, the master symmetry method and the relativistic invariance of the duality relations. For the 4-dimensional heavenly system, the duality problem is studied firstly by formal series symmetry approach. Two elegant commuting recursion operators of the heavenly equation are naturally appeared from the formal series symmetry approach such that the duality problem can also be studied by means of the recursion operators. |