Evaluate elementary symmetric polynomials

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Claudio Bellani
Claudio Bellani 2014-7-13
回答： Roger Stafford 2014-7-13
Given n variables x_1...x_n and given an integer 1<=k<=n, I'd like to evaluate the k-th elementary symmetric polynomial, as defined -for instance- here:
http://en.wikipedia.org/wiki/Elementary_symmetric_polynomial .
My attempt was to store x=[x_1,...x_n], to define a vector j=[] of length k and then to execute
for j(1)=1:n
for j(2)=j(i):n
...
for j(n)=j(k-1):n
e=e + x(j(1))*...*x(j(k));
end...end
How to replace the dots?

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采纳的回答

Roger Stafford
Roger Stafford 2014-7-13
Let v = [x_1,x_2,x_3,...,x_n] be a vector of the values of x_i.
e = sum(prod(nchoosek(v,k),2));

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