Why does QUADL in MATLAB 7.2 (R2006a) not work as well as QUAD8?

I am performing an integration that executes well in older versions of MATLAB using QUAD8. When I execute it with QUADL, it is much slower and gives the following warning regarding a singularity:

 Warning: Maximum function count exceeded; singularity likely.

 > In quadl at 98

and then returns incorrect results.

Answer 1

[MathWorks Support Team]

This result is most likely due to the default absolute error tolerance used for the QUADL function. Try setting a larger tolerance using the tol input to the QUADL function.

If QUADL is still returning incorrect results and if the values in your integrand have a large difference in magnitude, try renormalizing the values so that they are similar. Having values with such a large difference in magnitude in your integrand may cause an accumulation of roundoff errors in the QUADL algorithm.