GraphCalc3DS by flarn2006 is a simple graphing calculator that works with RPN equations.

Release notes:

Small release to fix a bug in version 1.5. The bug was that undefined values weren’t graphed properly (properly in this case being not at all) when the equation was entered in algebraic notation. Because of this bug, for example, sqrt(1-x^2) would appear as the top half of a circle like it should, except there would be two vertical lines on the sides. Version 1.5.1 fixes this bug.

https://gbatemp.net/threads/release-graphing-calculator.399078/