Re: Re: Condition/constraint problem
- To: mathgroup at smc.vnet.net
- Subject: [mg40976] Re: [mg40938] Re: Condition/constraint problem
- From: Bobby Treat <drmajorbob+MathGroup3528 at mailblocks.com>
- Date: Sat, 26 Apr 2003 03:26:19 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
Your explanation implies there IS no value for vx1'[t], but Mathematica
does compute one, when t is numeric. It's simply wrong.
vx1[t_] := 0.0015 + 0.0012 Sin[70 t] /; t < 5
vx2[t_] := 0.0015 + 0.0012 Sin[70 t]
vx1'[2.]
vx2'[2.]
0.00793433
-0.0166163
Bobby
-----Original Message-----
From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
To: mathgroup at smc.vnet.net
Subject: [mg40976] [mg40938] Re: Condition/constraint problem
Hi,
der derivative is complete right, since
Condition[] has no derivative
Dt[vx1[t]] evaluates to vx1'[t]
until you can tell Mathematica how to
find out
a) what the function value of vx1[t] for t>5 may be
b) to compute the derivative for t==5
c) determine when the symbol t in vx1[t] may be >5
Regards
Jens
Bamboo wrote:
>
> Dear all,
>
> I find a problem and don't know why. The input is as following.
> If a condiction(constraint) is set to the function, vx1[t],
> the derivative of vx1[t] is worng (fin1 is not equal to fin2).
> Any help welcome.
>
> vx1[t_] : = 0.0015 + 0.0012 Sin[70 t] /; t < 5
> vx2[t_] : = 0.0015 + 0.0012 Sin[70 t]
> fin1 = Dt[vx1[t], t]
> fin2 = Dt[vx2[t], t]
> Plot[fin1, {t, 0, 2}]
> Plot[fin2, {t, 0, 2}]
>
> Thanks,
> Bamboo