The reliability of the local error estimates returned by the Gauss-Kronrod
quadrature rules can be raised up to the theoretical 100% rate of success,
under error estimate sharpening, provided a number of natural validating co
nditions are required. The self-validating scheme of the local error estima
tes, which is easy to implement and adds little supplementary computing eff
ort, strengthens considerably the correctness of the decisions within the a
utomatic adaptive quadrature. (C) 2001 Elsevier Science B.V. All rights res
erved.