2019-09-28 20:37:14 +0100 received badge ● Notable Question (source) 2018-09-08 20:18:02 +0100 received badge ● Popular Question (source) 2017-02-20 19:58:54 +0100 commented answer help on using chain rule in Sage Great! I see that diff(w,t) at the end gives the same behavior I was observing above. Thanks! 2017-02-20 09:51:34 +0100 received badge ● Student (source) 2017-02-20 09:50:09 +0100 asked a question help on using chain rule in Sage Does anyone have any tips for using Sage to take derivatives of functions of many variables? For example, if I define w(x,y) = x^2 + y^2 (say) and then if I suppose that x and y depend on an independent variable t, the chain rule applies for finding w.diff(t). The only way I found to do this in Sage is var('t') x(t) = cos(t) (say) y(t) = sin(t) w(x,y) = x^2 + y^2 w.diff(t) But this isn't really using the chain rule. If I instead try var('x,y') (define w again) (define x and y again) w.diff(t) Out: (x,y) |--> 0 Apparently it thinks the derivative is zero because it still thinks x and y are two independent variables where they appear in w, even though you get x Out: t |--> cos(t) and similarly for y. Any suggestions? Thanks.