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Writing polynomial in the generators of a subring

asked 2024-12-22 13:58:57 +0100

schcs gravatar image

updated 2024-12-22 15:49:59 +0100

I have a polynomial $f\in\mathbb F[x_1,\ldots,x_n]$ and I know that it is an element of the subalgebra generated by $f_1,\ldots,f_k$. In fact, I can confirm this with f.in_subalgebra. However, I'd like the actual expression $h(t_1,\ldots,t_k)$ such that $f=h(f_1,\ldots,f_k)$. I know that the Groebner basis method should produce such $h$.

I'd like to know if there is a ready-to-use functionality in Sage to produce $h$.

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answered 2024-12-22 19:49:49 +0100

Max Alekseyev gravatar image

updated 2024-12-22 19:50:02 +0100

You can just borrow the code from in_subalgebra(algorithm="groebner"). It does compute the required polynomial (called z in the code), but does not return it.

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Many thanks. I feel that in future releases, it could be good to return the polynomial z also, since it might be useful for other users.

schcs gravatar imageschcs ( 2024-12-23 14:17:43 +0100 )edit

@schcs: please submit a feature request at https://github.com/sagemath/sage/issues

Max Alekseyev gravatar imageMax Alekseyev ( 2024-12-23 15:35:37 +0100 )edit

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Asked: 2024-12-22 13:58:57 +0100

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