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2016-02-17 11:45:17 -0500 answered a question Symmetric polynomial as a polynomial on elementary symmetric polynomials

The answer is actually implicit in the linked page: elementary functions have the property that (with Sage's notation) e[i, j, ...] = e[i]*e[j]*.... So there you have your polynomial.

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2016-02-17 11:40:15 -0500 commented answer Run multiple instances of Sage

Apparently you are right. I use Sage 7.0 on Debian unstable. I installed Sage unpacking the file distributed on Sage's website (for amd64). However, probably I did (by mistake) checkout another version and then checkout again versio 7.0. This might have corrupted something. I tried on another computer (same environment, but without that error with checkout) and it works. So probably it is my fault and that is the culprit.

2016-02-17 11:36:12 -0500 asked a question Substitute elementary symmetric functions in a polynomial

Suppose I do the following:

sage: SF=SymmetricFunctions(QQ)
sage: poly=SF.e()(SF.from_polynomial(x^2+y^2))
sage: poly
e[1, 1] - 2*e[2]

Now I would like to substitute e[1, 1] in that expression. However:

sage: poly.subs({SF.e()[1, 1]: 1})
e[1, 1] - 2*e[2]

Does not do what I want (in fact it does not do anything). Is there a way to substitute a specific elementary polynomial?

2016-02-17 10:34:38 -0500 asked a question Run multiple instances of Sage

Is it possible to run multiple instances of Sage? If I try, the second one complains that Sage crashed and lets me send a bug report. But Sage did not crash, it is just that another instance is going. Is it intended? Is there any workaround?

(I might use the notebook to do multiple things a time, I guess, but I really work better the the IPython console)

2016-02-17 07:56:39 -0500 commented question Prevent Sage from executing symbolic computation

Sure, that's a possibility, but I hoped not having to type the expression twice (my main aim was actually that of proof reading expressions in a more natural writing). Thanks anyway!

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2016-02-16 10:07:18 -0500 asked a question Symmetric polynomial as a polynomial on elementary symmetric polynomials

SymmetricFunctions, together with the various provided bases, is very good at writing a symmetric polynomial as the linear combination of what is called elementary functions here: mathworld.wolfram.com/SymmetricPolynomial.html. However, a different result says that a symmetric polynomial can be written as a polynomial on what is called elementary symmetric polynomials in the same paper. Can that be computed with Sage?

2016-02-16 07:19:18 -0500 commented question Prevent Sage from executing symbolic computation

I notice that some operations have a hold property that does it. But sum apparently has not. Is there a general solution?

2016-02-16 06:48:54 -0500 asked a question Prevent Sage from executing symbolic computation

Hi.

I would like to ask Sage not to perform a certain symbolic computation until I tell it to. This is because I would like first to show with view the thing I am typing, and then execute it later. So, for instance, I would like something like

sage: view(noexec(sum(1/k^4, k, 1, oo)))

(which should show the summation formula without executing it) and

sage: view(sum(1/k^4, k, 1, oo))

(which should show the result, as it actually does).

Is this possible?