Resummation
In mathematics and theoretical physics, resummation is a procedure to obtain a finite result from a divergent sum of functions. Resummation involves a definition of another function in which the individual terms defining the original function are re-scaled, and an integral transformation of this new function to obtain the original function. Borel resummation is probably the most well-known example.
The simplest method is an extension of a variational approach to higher order
based on a paper by R.P. Feynman and H. Kleinert.
In quantum mechanics it was extended to any order here, and in quantum field theory here.
See also Chapters 16–20 in the textbook cited below.Books
