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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).
Perturbation theory develops an expression for the desired solution in terms of a formal power series known as a perturbation series in some "small" parameter, that quantifies the deviation from the exactly solvable problem. The leading term in this power series is the solution of the exactly solvable problem, while further terms describe the ...
In a formal power series, the powers of the variable are used only as position-holders for the coefficients, so that the coefficient of is the fifth term in the sequence. In combinatorics, the method of generating functions uses formal power series to represent numerical sequences and multisets, for instance allowing concise expressions for ...
In mathematics, a power series (in one variable) is an infinite series of the form = = + + + … where represents the coefficient of the nth term and c is a constant called the center of the series. Power series are useful in mathematical analysis , where they arise as Taylor series of infinitely differentiable functions .
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 ...
In other words we can always find a (unique) power series G such that F(x,G(x)) = 0. A homomorphism from a formal group law F of dimension m to a formal group law G of dimension n is a collection f of n power series in m variables, such that G(f(x), f(y)) = f(F(x,y)).
Unlike an ordinary series, the formal power series is not required to converge: in fact, the generating function is not actually regarded as a function, and the "variable" remains an indeterminate. One can generalize to formal power series in more than one indeterminate, to encode information about infinite multi-dimensional arrays of numbers.
Recurrence relation, telescoping series; Generating functions as an application of formal power series. Cyclic sieving; Schrödinger method; Exponential generating function; Stanley's reciprocity theorem; Binomial coefficients and their properties; Combinatorial proof. Double counting (proof technique) Bijective proof; Inclusion–exclusion ...