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How to recover underlying vector space from quotient of polynomial ring

asked 1 year ago

updated 0 years ago

FrédéricC gravatar image

Suppose I'm working with the ring R = Q[x]/(x^20), and I have a collection of elements f_1, ..., f_10. I want to determine if these elements are linearly independent over Q, and if not, to determine the linear relations between them. I can't figure out how to recover the vector space underlying R from the ring R. Thanks!

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answered 1 year ago

Calling vector(...) on a ring element should work:

sage: S.<x> = QQ[]
sage: I = S.ideal(x**20)
sage: R = S.quotient(I)
sage: R.inject_variables()
Defining xbar
sage: f1 = xbar**2 + 3*xbar
sage: f2 = xbar**3 - xbar + 2
sage: vector(f1)
(0, 3, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0)
sage: vector(f2)
(2, -1, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0)

Now you can use any Sage tools from linear algebra to examine those vectors.

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Asked: 1 year ago

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Last updated: Jul 20 '23