Take the 2-minute tour ×
Mathematica Stack Exchange is a question and answer site for users of Mathematica. It's 100% free, no registration required.

I have a path V[t_]:={3t^2,2,6t}, and I define F[t_]:=V[t]/Norm[V[t]]. I simply want the derivative of F, which is a 3-vector function of the variable t. Somehow I did not manage to find any (simple?) way to calculate it.. Ideas?

share|improve this question
    
You might want to use V[t]/Sqrt[V[t].V[t]] instead. –  J. M. Apr 19 '13 at 8:35
    
Alternatively, you have to use Assuming or the Assumptions when you will simplify the derivative of the function F –  Spawn1701D Apr 19 '13 at 8:43
    
Thanks... I also didn't notice in my attempts.., that Mathematica was still complaining about an ancient error, hidden behind my window... –  Dror Apr 19 '13 at 8:48
    
@Dror And you are sure you want this instead of the normalized derivative of v, which is the direction vector along the path? –  halirutan Apr 19 '13 at 9:28
    
@halirutan , thanks for the nice tip. Though, In my case (which, regretfully, I did not specify), V is actually the derivative of my original path, and I wanted to find It's normal. –  Dror Apr 19 '13 at 10:25

1 Answer 1

You don't specified what your actual problem is and what exactly you have tried. Isn't this simple enough?

v[t_] := {3 t^2, 2, 6 t};
f[t_] := v[t]/Sqrt[v[t].v[t]]

D[f[t], t]
share|improve this answer
    
Yes, that works. Somehow It didn't work when using Norm[]. Thanks! (In my next questions, all will be specified! :) ) –  Dror Apr 19 '13 at 10:26

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.