A Characterization of the Orientations of Ternary Matroids
نویسندگان
چکیده
A matroid or oriented matroid is dyadic if it has a rational representation with all nonzero subde-terminants in ff2 k : k 2 Zg. Our main theorem is that an oriented matroid is dyadic if and only if the underlying matroid is ternary. A consequence of our theorem is the recent result of G. Whittle that a rational matroid is dyadic if and only if it is ternary. Along the way, we establish that each whirl has three inequivalent orientations. Furthermore, except for the rank-3 whirl, no pair of these are isomorphically equivalent. A rational matrix is totally dyadic if all of its nonzero subdeterminants are in D := ff2 k : k 2 Zg. A matroid or oriented matroid is dyadic if it can be represented over Q by a totally{dyadic matrix. It is easy to see that dyadic matroids are ternary, since elements of D map to nonzeros of GF(3) when viewed modulo 3 (see Lee (1990), for example). Hence the matroids that underlie dyadic oriented-matroids are ternary. Our main result is the \if" part of the following theorem (the \only if" part being the simple observation mentioned above).
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ورودعنوان ژورنال:
- J. Comb. Theory, Ser. B
دوره 77 شماره
صفحات -
تاریخ انتشار 1999