Bill Allombert on Tue, 27 Apr 2004 20:13:28 +0200

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Re: change variables in multivariant polynomials.

On Tue, Apr 27, 2004 at 12:27:36PM -0500, Ariel Pacetti wrote:
> >
> > Usually the proper way to rename z to w in g is to do
> > subst(g,z,w).
> >
> > changevar should never be used, it just does not work, it might
> > even be removed completly in the future.
> >
> I had the following problem (some time ago): if I have a polynomial (let's
> say in one variable) such that all the powers are even (multiples of 3, or
> whatever), how can I make something like:
> subst(g,x,x^(1/2)) ?
> Clearly this expresion makes sence just formally, but pari tries to
> compute "x^(1/2)" first. Is there a way to do this?
> Cheers,

With the development version you can just do subst(g,x^2,x) though this
particular use of subst will probably be renamed to substpol(g,x^2,x).

With the stable version, you can do lift(subst(g,x,Mod(x,x^2-a))) which
in effect do subst(g,x,a^(1/2)) by defining x as a^(1/2).