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asked 7 years ago

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Map between projective curves defined in an extension field

For example, suppose I have the following 2 projective curves:

k = GF(13)
x,y,z = ProjectiveSpace(k, 2, 'x,y,z').gens()
E = Curve(2*x^2 + 8*y*z + 8*z^2)
W = Curve(x^2 + y*z + z^2)

I like to define a map from E to W that involves 2 and 8, which do not exist in k = GF(13), but do in an extension of k:

x = PolynomialRing(k,'x').gen()
K = GF(13**2, 'w', modulus=x^2-2)
w = K.gen()

So w=2 and 2w=8. The map I like to define sends (x:y:z) to (wx:2wy:2wz).

In this particular example, it's obvious that (wx:2wy:2wz)=(x:2y:2z); but it's just a simple example do demonstrate the problem.

Something like this doesn't work:

x,y,z = ProjectiveSpace(k, 2, 'x,y,z').gens() #or ProjectiveSpace(K, 2, 'x,y,z').gens()
E.Hom(W)([w*x, 2*w*y, 2*w*z])

Thank you.

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updated 5 years ago

FrédéricC gravatar image

Map between projective curves defined in an extension field

For example, suppose I have the following 2 projective curves:

k = GF(13)
x,y,z = ProjectiveSpace(k, 2, 'x,y,z').gens()
E = Curve(2*x^2 + 8*y*z + 8*z^2)
W = Curve(x^2 + y*z + z^2)

I like to define a map from E to W that involves 2 and 8, which do not exist in k = GF(13), but do in an extension of k:

x = PolynomialRing(k,'x').gen()
K = GF(13**2, 'w', modulus=x^2-2)
w = K.gen()

So w=2 and 2w=8. The map I like to define sends (x:y:z) to (wx:2wy:2wz).

In this particular example, it's obvious that (wx:2wy:2wz)=(x:2y:2z); but it's just a simple example do demonstrate the problem.

Something like this doesn't work:

x,y,z = ProjectiveSpace(k, 2, 'x,y,z').gens() #or ProjectiveSpace(K, 2, 'x,y,z').gens()
E.Hom(W)([w*x, 2*w*y, 2*w*z])

Thank you.