Borel's Methods of Summability

Summability methods are concerned with transforming series of numbers to other series. It is an area that has seen applications in number theory as well as in other parts of mathematics. This book covers both the theory and some of the applications of Borel summability.

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Summability methods are transformations that map sequences (or functions) to sequences (or functions). A prime requirement for a "good" summability method is that it preserves convergence. Unless it is the identity transformation, it will do more: it will transform some divergent sequences to convergent sequences.

An important type of theorem is called a Tauberian theorem. Here, we know that a sequence is summable. The sequence satisfies a further property that implies convergence.

Borel's methods are fundamental to a whole class of sequences to function methods. The transformation gives a function that is usually analytic in a large part of the complex plane, leading to a method for analytic continuation.

These methods, dated from the beginning of the 20th century, have recently found applications in some problems in theoretical physics.