# p-Adic Extension Element¶

A common superclass for all elements of extension rings and field of Zp and Qp.

AUTHORS:

• David Roe

INPUT:

• parent - a SageObject
frobenius(arithmetic=True)

Returns the image of this element under the Frobenius automorphism applied to its parent.

INPUT:

• self – an element of an unramified extension.
• arithmetic – whether to apply the arithmetic Frobenius (acting by raising to the $$p$$-th power on the residue field). If False is provided, the image of geometric Frobenius (raising to the $$(1/p)$$-th power on the residue field) will be returned instead.

EXAMPLES:

sage: R.<a> = Zq(5^4,3)
sage: a.frobenius()
(a^3 + a^2 + 3*a) + (3*a + 1)*5 + (2*a^3 + 2*a^2 + 2*a)*5^2 + O(5^3)
sage: f = R.defining_polynomial()
sage: f(a)
O(5^3)
sage: f(a.frobenius())
O(5^3)
sage: for i in range(4): a = a.frobenius()
sage: a
a + O(5^3)

sage: K.<a> = Qq(7^3,4)
sage: b = (a+1)/7
sage: c = b.frobenius(); c
(3*a^2 + 5*a + 1)*7^-1 + (6*a^2 + 6*a + 6) + (4*a^2 + 3*a + 4)*7 + (6*a^2 + a + 6)*7^2 + O(7^3)
sage: c.frobenius().frobenius()
(a + 1)*7^-1 + O(7^3)


An error will be raised if the parent of self is a ramified extension:

sage: K.<a> = Qp(5).extension(x^2 - 5)
sage: a.frobenius()
Traceback (most recent call last):
...
NotImplementedError: Frobenius automorphism only implemented for unramified extensions


#### Previous topic

$$p$$-Adic ZZ_pX Element