Is it possible to export an excel file created on the fly to include formulas?
I already know about adding the header with application/vnd.ms-excel or just exporting as a csv. Is there a way to have a formula exported that allows the user to change data in the sheet and auto sum via a formula?
The server side language in this case would be php.
I have only ever used the native php library to do excel functions including saving formulas. If you want to look at alternatives I would take a look at this one. It seems to do what you want.