Calculator freehand complex scientific equations

Richard429

I am looking for an app or software that performs as a calculator and uses a stylus only for input, allowing the user to write complex equations on the screen of a smart device. The device then recognises the formula and performs the calculation. Capable maybe, for example, of writing Lane–Emden equation and then plotting solution. Not hung up on L-E eq but used as example only. Should also be capable of roll back roll forward.

Appreciate any feedback
Richard