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A formal power series can be loosely thought of as an object that is like a polynomial, but with infinitely many terms.Alternatively, for those familiar with power series (or Taylor series), one may think of a formal power series as a power series in which we ignore questions of convergence by not assuming that the variable X denotes any numerical value (not even an unknown value).
Its formal group ring (also called its hyperalgebra or its covariant bialgebra) is a cocommutative Hopf algebra H constructed as follows. As an R-module, H is free with a basis 1 = D (0), D (1), D (2), ... The coproduct Δ is given by ΔD (n) = ΣD (i) ⊗ D (n−i) (so the dual of this coalgebra is just the ring of formal power series).
The ring of formal power series over the complex numbers is a UFD, but the subring of those that converge everywhere, in other words the ring of entire functions in a single complex variable, is not a UFD, since there exist entire functions with an infinity of zeros, and thus an infinity of irreducible factors, while a UFD factorization must be ...
[4] K[[X]], the ring of formal power series over the field K. For each nonzero power series P, define f (P) as the order of P, that is the degree of the smallest power of X occurring in P. In particular, for two nonzero power series P and Q, f (P) ≤ f (Q) if and only if P divides Q. Any discrete valuation ring.
pronounced "R I hat". The kernel of the canonical map π from the ring to its completion is the intersection of the powers of I. Thus π is injective if and only if this intersection reduces to the zero element of the ring; by the Krull intersection theorem, this is the case for any commutative Noetherian ring which is an integral domain or a ...
The field of formal Laurent series over a field k: (()) = [[]] (it is the field of fractions of the formal power series ring [[]]. The function field of an algebraic variety over a field k is lim → k [ U ] {\displaystyle \varinjlim k[U]} where the limit runs over all the coordinate rings k [ U ] of nonempty open subsets U (more ...
the ring of formal power series over any field; For a given DVR, one often passes to its completion, a complete DVR containing the given ring that is often easier to study. This completion procedure can be thought of in a geometrical way as passing from rational functions to power series, or from rational numbers to the reals.
This is slightly oversimplified. The Tate curve is really a curve over a formal power series ring rather than a curve over C. Intuitively, it is a family of curves depending on a formal parameter. When that formal parameter is zero it degenerates to a pinched torus, and when it is nonzero it is a torus).