Bill Allombert on Mon, 24 Sep 2012 16:23:40 +0200 |
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Re: How to overcome limitations on variable names in PARI-GP |
On Mon, Sep 24, 2012 at 03:18:43PM +0200, Ewan Delanoy wrote: > Hello all, > > ? > ? trial1=polinv(proposer,modulus,x) > %4 = (282*a^3 + 280*a)*x + (-1407*a^4 - 1765*a^2 - 300) > ? > ? /*the result above is correct. Now see what happens when we replace x with a : */ > ? > ? proposer=(-282*a^3 - 280*a)*b + (285*a^4 - 85*a^2 - 300) > %5 = 285*a^4 - 282*b*a^3 - 85*a^2 - 280*b*a - 300 Hello Ewan, You did not replace x by a, but by b. What happen is that x has a higher priority than a, but b has a lower priority than a. So instead of working in K(a)[x] you are now in K(b)[a]. So the notion of degree and Euclidean divisions etc. are different. Fundamentally PARI only know about univariate polynomials over fields. If you add b; on the first line of your program, it should work, by forcing b to have an higher priority than x. The documentation of variable priorities is available by entering in GP: ??"Variable priorities, multivariate objects"@2 Cheers, Bill.