Re: Evaluate[expr]
- To: mathgroup at smc.vnet.net
- Subject: [mg123461] Re: Evaluate[expr]
- From: DrMajorBob <btreat1 at austin.rr.com>
- Date: Thu, 8 Dec 2011 05:23:44 -0500 (EST)
- Delivered-to: l-mathgroup@mail-archive0.wolfram.com
- References: <201112071114.GAA04233@smc.vnet.net>
- Reply-to: drmajorbob at yahoo.com
It doesn't work without Evaluate because:
Attributes@Table
{HoldAll, Protected}
HoldAll prevents arguments being evaluated (unless you include Evaluate)
until too late in Table's evaluation. When x has a value -- the definition
of too late in this case -- D[f[x], x] makes no sense. When x is 0., for
instance:
D[f[0.], 0.]
\!\(
\*SubscriptBox[\(\[PartialD]\), \(0.`\)]1.`\)
General::ivar: 0.` is not a valid variable. >>
Bobby
On Wed, 07 Dec 2011 05:14:45 -0600, é?? å?? <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]?
>
> Can you help me?
>
--
DrMajorBob at yahoo.com
- References:
- Evaluate[expr]
- From: é å <shlwell1988@gmail.com>
- Evaluate[expr]