Only part of the method works. More doctoring is needed.
For this example [double integration] simplex spits out
more decimals than the ∫(f,n,s) operator => 0.5s/42s
~ 80 times faster @ higher accuracy !

The original Mathcad 8 from Guiseppe Borzi is added for Doctoring.
Thanks again Carlos for enabling the recursive.

Jean

Maths Simplex_fix [Carlos] Copy.sm (84 KiB) downloaded 70 time(s).

Maths Simplex MCD.sm (125 KiB) downloaded 75 time(s).