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A series is convergent (or converges) if and only if the sequence (,,, … ) {\displaystyle (S_{1},S_{2},S_{3},\dots )} of its partial sums tends to a limit ; that means that, when adding one a k {\displaystyle a_{k}} after the other in the order given by the indices , one gets partial sums that become closer and closer to a given number.
There is a theorem which states that, if the sum of over is absolutely convergent, then takes non-zero values on a set that is at most countable. Therefore, the following is a consistent definition of the sum of over when the sum is absolutely convergent.
= + = + +, which has a sum of the natural logarithm of 2, while the sum of the absolute values of the terms is the harmonic series, = = + + + + +, which diverges per the divergence of the harmonic series, [28] so the alternating harmonic series is conditionally convergent.
Therefore, the sum converges if and only if the integral over the same range of the same function converges. When this equivalence is used to check the convergence of a sum by replacing it with an easier integral, it is known as the integral test for convergence .
In mathematics, convergence tests are methods of testing for the convergence, conditional convergence, ... converges if and only if the sum = = converges ...
Thus, the sum of the purple squares' area is one-third of the area of the large square. When summing infinitely many terms, the geometric series can either be convergent or divergent. Convergence means there is a value after summing infinitely many terms, whereas divergence means no value after summing.
A sequence of functions () converges uniformly to when for arbitrary small there is an index such that the graph of is in the -tube around f whenever . The limit of a sequence of continuous functions does not have to be continuous: the sequence of functions () = (marked in green and blue) converges pointwise over the entire domain, but the limit function is discontinuous (marked in red).
Absolutely convergent series are unconditionally convergent. But the Riemann series theorem states that conditionally convergent series can be rearranged to create arbitrary convergence. [4] Agnew's theorem describes rearrangements that preserve convergence for all convergent series. The general principle is that addition of infinite sums is ...