Difference between revisions of "Symmetric sum"

(Made latex look better.)
Line 1: Line 1:
A '''symmetric sum''' is any sum in which any [[permutation]] of the variables leaves the sum unchanged.
+
The '''symmetric sum''' <math>\sum_{sym} f(x_1, x_2, x_3, \dots, x_n)</math> of a function <math>f(x_1, x_2, x_3, \dots, x_n)</math> of <math>n</math> variables is defined to be <math>\sum_{\sigma} f(x_{\sigma(1)}, x_{\sigma(2)}, x_{\sigma(3)}, \dots, x_{\sigma(n)})</math>, where <math>\sigma</math> ranges over all permutations of <math>(1, 2, 3, \dots, n)</math>.  More generally, a '''symmetric sum''' of <math>n</math> variables is any sum that is unchanged by any [[permutation]] of its variables.  More generally still, a '''symmetric function''' of <math>n</math> variables is any function that is unchanged by any [[permutation]] of its variables.
  
One way to generate symmetric sums is using symmetric sum notation. If <math>f(x_1, x_2, x_3, \dots, x_n)</math> is a function of <math>n</math> variables then the symmetric sum <math>\sum_{sym} f(x_1, x_2, x_3, \dots, x_n) = \sum_{\sigma} f(x_{\sigma(1)}, x_{\sigma(2)}, x_{\sigma(3)}, \dots, x_{\sigma(n)})</math>, where <math>\sigma</math> ranges over all permutations of <math>(1, 2, 3, \dots, n)</math>.
+
Any symmetric sum can be written as a polynomial of [[elementary symmetric sum]]s.
 
 
All symmetric sums can be written as a polynomial of [[elementary symmetric sum]]s.  
 
  
 
== See also==
 
== See also==

Revision as of 14:37, 17 June 2018

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 any sum that is unchanged by any permutation of its variables. More generally still, a symmetric function of $n$ variables is any function that is unchanged by any permutation of its variables.

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.