Considered one of the TOP 50 IPAD APPS at http://www.top10onlineuniversities.org/top-50-ipad-apps-for-e-learners.html
FxIntegrator is a mathematical tool that evaluates the area under a function curve for a given interval.

It's extremely handy for math students or engineers who need to calculate integrals using an iPad or iPhone.
Unlike other calculators, its elegant function editor makes it possible to write expressions in natural mathematical notation. It's a dream come true.

FEATURES
✔ Natural expression editor: write your functions just like they appear in math textbooks.
✔ Three integration methods to choose from: rectangle, trapezoidal, Simpson.
✔ Finite or infinite boundaries: compute improper integrals just as easily as proper integrals.
✔ Adaptive approximation: get results faster for most functions while maintaining accuracy for difficult functions.
✔ Built-in functions supported: acos, acosh, asin, asinh, atan, atanh, cos, cosh, ln, log, sign, sin, sinh, tan, tanh, square root, absolute value.
✔ Displays the computation time used.

fxIntegrator was officially recommended by Utrecht University: http://www.uu.nl/university/library/NL/informatie/tablets/Pages/default.aspx

fxIntegrator was considered an excellent teaching tool by the University of British Columbia: http://wiki.ubc.ca/Course%3aETEC522/sept2011/Ipads

REVIEWS
http://www.walkingrandomly.com/?p=2692
http://www.fleischer.se/blogg/2010/12/01/undervisar-du-i-matematik-har-ar-ipad-apparna-for-dig/