Re: Evaluate[expr]
- To: mathgroup at smc.vnet.net
- Subject: [mg123456] Re: Evaluate[expr]
- From: Bill Rowe <readnews at sbcglobal.net>
- Date: Thu, 8 Dec 2011 05:22:47 -0500 (EST)
- Delivered-to: l-mathgroup@mail-archive0.wolfram.com
On 12/7/11 at 6:14 AM, shlwell1988 at gmail.com wrote:
>f[x_] = x^5 - 3 x^2 + 1; tt =
>Table[Evaluate[{{x}, f[x], D[f[x], x]}], {x, 0, 2, 0.3}]
>In the above expression , what's the function of Evaluate[expr]?
>Why doesn't it work without Evaluate[expr]?
Evaluate forces immediate evaluation of any expression it is
given. Without Evaluate, a value is assigned to x then the
derivative you want is computed. That is, when x is zero,
D[f[x],x] evaluates to D[f[0],0] which makes no sense.
With Evaluate D[f[x],x] is evaluated to 5x^4-6x and this is
evaluated after x is assigned a value which is what you want.