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). Cheers, Bill.