MathGroup Archive 2004

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

Search the Archive

Re: Forcing a Derivative

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

"Scott Guthery" <sguthery at> wrote in message news:<cijej8$hlp$1 at>...
> 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


  • 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