@@ -1195,8 +1195,7 @@ def to_cycles(self, singletons=True, use_min=True, negative_cycles=True):
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The cycles are returned in the order of increasing smallest
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elements, and each cycle is returned as a tuple which starts
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- with its smallest positive element. We do not include the
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- corresponding negative cycles.
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+ with its smallest positive element.
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INPUT:
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@@ -1269,13 +1268,22 @@ def cycle_type(self):
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Return a pair of partitions of ``len(self)`` corresponding to the
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signed cycle type of ``self``.
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- A *negative cycle* is a cycle `C = (c_0, \ldots, c_{2k-1})` such that
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- `c_0 = c_k`. Any other cycle is positive. For any cycle `C`, we
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- ignore the cycle `-C` (provided this is a different cycle).
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+ A *cycle* is a tuple `C = (c_0, \ldots, c_k)` with `\pi(c_i) = c_{i+1}`
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+ for `0 \leq i < k` and `\pi(c_k) = c_0`. If `C` is a cycle,
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+ `\overline{C} = (-c_0, \ldots, -c_k)` is also a cycle. A cycle is
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+ *negative*, if `C = \overline{C}` up to cyclic reordering. In this
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+ case, `k` is necessarily even and the length of `C` is `k/2`.
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+ A *positive cycle* is a pair `C \overline{C}`, its length is `k`.
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+
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+ Let `\alpha` be the partition whose parts are the lengths of the
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+ positive cycles and let `\beta` be the partition whose parts are
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+ the lengths of the negative cycles. Then `(\alpha, \beta)` is
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+ the cycle type of `\pi`.
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EXAMPLES::
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- sage: pi = SignedPermutations(7)([2,-1,4,-6,-5,-3,7])
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+ sage: G = SignedPermutations(7)
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+ sage: pi = G([2, -1, 4, -6, -5, -3, 7])
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sage: pi.cycle_type()
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([3, 1], [2, 1])
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