I've started to reach a point where working out problems on my sketch pad is becoming impractical. In classical mechanics in particular, it feels like I'm spending a lot of time doing "grunt work" like working out derivatives or integrals, or making conversions to new variables. It feels like I'm spending much more time on the algebra and calculus computation than I am on the physics. It's not difficult, but it's a time sink. Plus my hand starts to cramp from all of the writing. So what I'm looking for is something that can do things like quickly take integrals and derivatives of expressions, change variables in an expression, and do algebra on an equation. Ideally, if it could keep a LaTeX picture of the expression I'm working on open, that would be even better. Suggestions?