Integral dx/sqrt(1+x^3)

[parisse]

Perhaps the message is misleading, the adaptative method (gaussian quadrature) fails but not much (error estimate is about 1e-9, greater than epsilon), while Romberg fails totally. I can probably issue another error message in the terminal with the error estimate.
(For my own usage, this is in intg.cc/tegral(const...)/
if (A==C || B==C)
return false; // can not subdivise anymore
)