Re: Newbie mathematica question

• To: mathgroup at smc.vnet.net
• Subject: [mg37157] Re: [mg37123] Newbie mathematica question
• From: purcell <chris.purcell at drdc-rddc.gc.ca>
• Date: Sun, 13 Oct 2002 05:57:03 -0400 (EDT)
• Sender: owner-wri-mathgroup at wolfram.com

```If you use SetDelayed rather than Set, and then Simplify, Mathematica

f[t_] := {t + Sqrt[3] Sin[t], 2 Cos[t], t Sqrt[3] - Sin[t]} ;
Simplify[Sqrt[f'[t] .f'[t]]]

Out[2]= 2 Sqrt[2]

>Hi, I have defined a function from R -> R^3 as follows: f[t_] = {t +
>Sqrt[3] Sin[t], 2 Cos[t], t Sqrt[3] - Sin[t]} So It's basically a vector
>whose coordinates are determined based on the values you pass in. Then I
>took the derivative by just typing f', which outputs {1 + Sqrt[3] Cos[#1],
>-2 Sin[#1], Sqrt[3] - Cos[#1]}& What I'd like to do is have Mathematica
>calculate the norm of this as it would any vector, so that I can play with
>the norm function. As it turns out, the norm in this case is identical to
>Sqrt[8], so it would be nice if Mathematica could figure that out. Is it
>possible to do this? Thanks

Christopher J. Purcell