Schwinger-Lanczos algorithm for calculation of off-shell T-matrix elements and Wynn's epsilon algorithm.

**Abstract:**

A generalization of the Schwinger-Lanczos algorithm
for the calculation of the off-shell T-matrix elements is presented and
shown to be equivalent to the Wynn's

epsilon algorithm for acceleration of the Born
series. Both methods are applied to the calculation of cross section for
the dissociative attachment of electrons to

hydrogen molecule, e(-) + H-2 --> H + H-. Although
formally fully equivalent both methods behave very differently numerically.
It is shown that the

Schwinger-Lanczos algorithm is more stable and
generally superior to ail other methods discussed in this paper.