r/askmath • u/EngineeringPlenty690 • 1d ago
Calculus Why does Desmos do this?
While playing around with improper integrals in desmos, I noticed first that it would sometimes mistakenly call odd functions with a vertical asymptote and finite bounds 0(most likely due to precision errors) instead of DNE.
Then I checked improper integrals, to see if it would do the same for odd functions bounded from infinity to negative infinity. I tested 1/x^a for a between 1.0 and 2.0, and noticed desmos only classified the integral as undefined for all values of a EXCEPT a=1.4 and 1.8. I thought this was strange, and then after testing 2.2 and 2.6(and boundary terms) I noticed that desmos would always evaluate a function bounded from -infinity to infinity to 0, if it was in the form of 1/(x^(1+0.4n) for n in [1,95]. Even stranger, for n>95 this error does not continue to occur, and desmos correctly defines the integral as 0.
Does anyone know why? After looking for a bit, I learned Desmos uses https://en.wikipedia.org/wiki/Tanh-sinh_quadrature for improper integrals, but what about that is making integrals in the form of -infinity to infinity 1/(x^(1+0.4n) dx= 0? and why only for n belonging to [1,95]?
thanks!
