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The following polynomials in two variables X 1 and X 2 are symmetric: + + + + (+) as is the following polynomial in three variables X 1, X 2, X 3: . There are many ways to make specific symmetric polynomials in any number of variables (see the various types below).
The cycle index polynomial of a permutation group is the average of the cycle index monomials of its elements. The phrase cycle indicator is also sometimes used in place of cycle index . Knowing the cycle index polynomial of a permutation group, one can enumerate equivalence classes due to the group 's action .
Note that 3 is a factor of 6.) The number of such polynomials is the index in the symmetric group S n of the subgroup H of permutations that preserve the polynomial. (For the example of x + y − z, the subgroup H in S 3 contains the identity and the transposition (x y).) So the size of H divides n!. With the later development of abstract ...
Aside from polynomial functions, tensors that act as functions of several vectors can be symmetric, and in fact the space of symmetric -tensors on a vector space is isomorphic to the space of homogeneous polynomials of degree on . Symmetric functions should not be confused with even and odd functions, which have a different sort of symmetry.
Galois' theory originated in the study of symmetric functions – the coefficients of a monic polynomial are (up to sign) the elementary symmetric polynomials in the roots. For instance, ( x – a )( x – b ) = x 2 – ( a + b ) x + ab , where 1, a + b and ab are the elementary polynomials of degree 0, 1 and 2 in two variables.
Cycles that contain a non-prime number of elements have cyclic subgroups that are not shown in the graph. For the group Dih 4 above, we could draw a line between a 2 and e since ( a 2 ) 2 = e , but since a 2 is part of a larger cycle, this is not an edge of the cycle graph.
Symmetric polynomials arise naturally in the study of the relation between the roots of a polynomial in one variable and its coefficients, since the coefficients can be given by polynomial expressions in the roots, and all roots play a similar role in this setting. From this point of view, the elementary symmetric polynomials are the most ...
Alternatively, a cycle with n elements is also a Z n-torsor: a set with a free transitive action by a finite cyclic group. [1] Another formulation is to make X into the standard directed cycle graph on n vertices, by some matching of elements to vertices. It can be instinctive to use cyclic orders for symmetric functions, for example as in xy ...