Symmetric sum

Revision as of 14:53, 17 June 2018 by Mathematrucker (talk | contribs) (Added in the definition of symmetric function and cleaned things up a bit.)

The symmetric sum $\sum_{sym} f(x_1, x_2, x_3, \dots, x_n)$ of a function $f(x_1, x_2, x_3, \dots, x_n)$ of $n$ variables is defined to be $\sum_{\sigma} f(x_{\sigma(1)}, x_{\sigma(2)}, x_{\sigma(3)}, \dots, x_{\sigma(n)})$, where $\sigma$ ranges over all permutations of $(1, 2, 3, \dots, n)$. More generally, a symmetric sum of $n$ variables is a sum that is unchanged by any permutation of its variables. More generally still, a symmetric function of $n$ variables is a function that is unchanged by any permutation of its variables.

Thus, the symmetric sum of a symmetric function $f(x_1, x_2, x_3, \dots, x_n)$ satisfies \[\sum_{sym} f(x_1, x_2, x_3, \dots, x_n) = n!f(x_1, x_2, x_3, \dots, x_n).\]

Any symmetric sum can be written as a polynomial of elementary symmetric sums.

See also

This article is a stub. Help us out by expanding it.