Re: Evaluate[expr]
- To: mathgroup at smc.vnet.net
- Subject: [mg123470] Re: Evaluate[expr]
- From: Murray Eisenberg <murray at math.umass.edu>
- Date: Thu, 8 Dec 2011 05:25:30 -0500 (EST)
- Delivered-to: l-mathgroup@mail-archive0.wolfram.com
- References: <201112071114.GAA04233@smc.vnet.net>
- Reply-to: murray at math.umass.edu
Because if you leave it out, what you're sking to do is, among other
things, to calculate D[f[0],0], D[f[0.3], 0.3], D[f[0.6],0.6], etc.
That's why you'll get a series of error messages beginning with
"General::ivar: 0.` is not a valid variable".
The Evaluate expression -- here could be wrapped just around the part
D[f[x],x]] -- once and for all evaluates the symbolic derivative. Then
the iterator in the table substitutes x = 0, 0.3, 0.6, etc. into that
symbolic derivative.
On 12/7/11 6:14 AM, =E9=81=93 =E5=8E=9A 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]?
>
> Can you help me?
>
--
Murray Eisenberg murray at math.umass.edu
Mathematics & Statistics Dept.
Lederle Graduate Research Tower phone 413 549-1020 (H)
University of Massachusetts 413 545-2859 (W)
710 North Pleasant Street fax 413 545-1801
Amherst, MA 01003-9305
- References:
- Evaluate[expr]
- From: é å <shlwell1988@gmail.com>
- Evaluate[expr]