Formula Engine Suggestions?

I'm currently designing the formula engine. At the moment it works on very simple maths expressions, but i wonder whether people would like to suggest things to add to it.
At the moment, i'm planning:
sin,cos,tan,arcsin etc
arctan2
power
sawtooth
and a few more i can't remember. if anyone wants to suggest stuff, feel free. Remember the engine also contains custom variables, FOR loops, proper IF and DO...WHILE statements.
At the moment, i'm planning:
sin,cos,tan,arcsin etc
arctan2
power
sawtooth
and a few more i can't remember. if anyone wants to suggest stuff, feel free. Remember the engine also contains custom variables, FOR loops, proper IF and DO...WHILE statements.