How to organise Tolerance problem in integration?

[Vanroose Wim <vanroose at ruca dot ua dot ac dot be>]

Dear GSL-users,

            I am using  the integration package "gsl_integration_qag" to
calculate  matrix  elements of a potential between two oscillator eigen
functions.    So of each   n and m I obtain a matrix element  <n|V|m>.

            Problem is  dat  <n|V|m> decreases with n and m  and from a
certain point it is a small a 10e-13.     For these high  matrix
elements.   The integration program start to protest  and mentions
"ERROR roundoff error prevents tolerance from being achieved".

            So how do I organise  a program that results into a 0 when
the upperbound is smaller than a certain threshold.


Best Wishes

Wim Vanroose