Services & Resources / Wolfram Forums
-----
 /
MathGroup Archive
2004
*January
*February
*March
*April
*May
*June
*July
*August
*September
*October
*November
*December
*Archive Index
*Ask about this page
*Print this page
*Give us feedback
*Sign up for the Wolfram Insider

MathGroup Archive 2004

[Date Index] [Thread Index] [Author Index]

Search the Archive

Re: Forcing a Derivative

  • To: mathgroup at smc.vnet.net
  • Subject: [mg50774] Re: Forcing a Derivative
  • From: p-valko at tamu.edu (Peter Valko)
  • Date: Sun, 19 Sep 2004 21:39:44 -0400 (EDT)
  • References: <cijej8$hlp$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

"Scott Guthery" <sguthery at mobile-mind.com> wrote in message news:<cijej8$hlp$1 at smc.vnet.net>...
> How does one force Derivative[n] to actually take the derivative?
> 
> For example if ...
> 
> f[x_] = x^2 + 7
> 
> g[x_]=3x^3 + 23
> 
> then
> 
> Derivative[2][f * g]
> 
> just puts a couple of primes on the product rather than actually computing the dervative.
> 
> Thanks for any insight.
> 
> Cheers, Scott


Help says:
"Whenever Derivative[n][f] is generated, Mathematica rewrites it as
D[f[#]&, {#, n}]. If Mathematica finds an explicit value for this
derivative, it returns this value. Otherwise, it returns the original
Derivative form."
Therefore, it is perhaps better to write staright:

D[f [x]* g[x],{x,2}]

and the result will be (after Simplify):

46 + 126*x + 60*x^3

Peter


  • Prev by Date: Re: Newbie Plot Question
  • Next by Date: Re: Newbie Plot Question
  • Previous by thread: Re: Re: Re: Re: Re: Forcing a Derivative
  • Next by thread: Re: Forcing a Derivative