The test function looks naive, it is not so. Ordinary Simpson 7½ D.
Same test function in the transformed domain boosts accuracy to 14½ D.

That would greatly enhance Smath vs competition.
I spare many hours trying to code Romberg, what a f...n mess.
Rather deceiving, though sometimes as good as Adaptive
RemToDo if I can convince myself !

Jean

Integrate Simplex QUICK [Simpson Domain].sm (20.92 KiB) downloaded 609 time(s).

... don't miss the 2nd example ... most remarkable for SimpsonTransform

Integrate Simplex QUICK [Simpson Domain] Copy.sm (28.45 KiB) downloaded 621 time(s).