Re: Failure to Evaluate?
- To: mathgroup at smc.vnet.net
- Subject: [mg49857] Re: Failure to Evaluate?
- From: Bill Rowe <readnewsciv at earthlink.net>
- Date: Wed, 4 Aug 2004 10:46:36 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
On 8/3/04 at 1:11 AM, sguthery at mobile-mind.com (Scott Guthery) wrote: >f:=Function[#1^2/#1+1] >g:=Function[#1^4+7] >h:=D[f]/D[g] >h >Gives >((#1^2/#1)+1 &)/(#1^4+7 &) >Why doesn't it evaluate by setting #1 to 1 to get 1/4? Because that would not necessarily be the correct answer. You defined h as the derivative of f divided by the derivative of g but failed to specify what the derivative was with respect to. That is D takes two arguments, the function to differentiate and a variable, i.e., D[x+2 y, x] != D[x+ 2 y, y] Since you didn't supply D with sufficient information, it returned the only argument you supplied it unevaluated, which is exactly what you see in the answer. -- To reply via email subtract one hundred and four