change variables in multivariant polynomials.

[Thomas Geffers <pmytg@maths.nottingham.ac.uk>]

Hi everyone!

I am a newbee and I have the following problem:

I am writing a program with gp with multivariant polynomials. Because of
the order of the variables I would like to change all the variables from 
the input-polynomials. But my way is not very elegant (and by the way does 
not work very good;-).

ie:
g=(u^4-4*u)*z^4 + u*z^2 -1;

variable(g) is now u. I get the other variable with 

variable(Vec(g));  \\ It gives the correct z.

My problem is, that I can not change this variable with changevar.
I "solve" this problem with a loop with the following kernel:

Pol(Vec(g)[i],w)  \\ hence for each coefficient.

As in the docomentation written, this can lead to invalid objects.
Is there a more elegant (correct?) way to solve this?

I know, that PARI/GP treats multivariant polynomials as univariant 
polynomials with polynomial coefficients, but is there a possiblity to get 
all variables at once?

Thank you very much,

Thomas Geffers  



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