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Solving equation with algebraic numbers

asked 2020-08-10 15:23:58 +0200

creyesm1992 gravatar image

Hello, SAGE gives me error when I load this: solve(x^2-AA(sqrt(3))==0,x) but it gives no problem when I load solve(x^2-sqrt(3)==0,x) This is a small example of a bigger problem I have in which I must solve a system of equations involving algebraic numbers through AA(.) and QQbar(.). How can I make SAGE solve equations with this type of numbers? or there is no way? Thanks!

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You can convert algebraic numbers to symbolic expressions using SR(...). Probably you would rather want to define an ideal in a polynomial ring, and compute a Gröbner basis and/or the associated variety (if the system has finitely many solutions). Can you add the system you actually want to solve?

rburing gravatar imagerburing ( 2020-08-10 16:08:59 +0200 )edit

Hello rburing, i tried loading solve(x^2-SR(AA(sqrt(3)))==0,x) but it gives error, what do you think?

creyesm1992 gravatar imagecreyesm1992 ( 2020-08-10 17:18:05 +0200 )edit

It seems Maxima can't handle the symbolic wrapper around AA elements. Try SR(AA(sqrt(3))).numerical_approx() for numerics, or AA(sqrt(3)).radical_expression() for an exact expression. Not all algebraics are expressible in terms of radicals, so this is not a good approach in general. Also solve may return only approximate solutions in more complicated cases. I would instead create an ideal I in a polynomial ring and call I.variety(AA) or I.variety(QQbar).

rburing gravatar imagerburing ( 2020-08-10 19:12:20 +0200 )edit

thanks rburing!

creyesm1992 gravatar imagecreyesm1992 ( 2020-08-11 23:09:25 +0200 )edit

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answered 2020-08-11 09:25:14 +0200

Emmanuel Charpentier gravatar image

A possible one-liner :

sage: (AA["x"](x^2-AA(sqrt(3)))).roots()

which can be abrbreviated as

sage: (x^2-AA(sqrt(3))).polynomial(AA).roots()


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thanks Emmanuel!

creyesm1992 gravatar imagecreyesm1992 ( 2020-08-11 23:09:10 +0200 )edit

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Asked: 2020-08-10 15:23:58 +0200

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Last updated: Aug 11 '20