Re: Re: Condition/constraint problem
- To: mathgroup at smc.vnet.net
- Subject: [mg40987] Re: Re: Condition/constraint problem
- From: "Peltio" <peltio at twilight.zone>
- Date: Sun, 27 Apr 2003 03:19:03 -0400 (EDT)
- References: <b8dclt$t99$1@smc.vnet.net>
- Reply-to: "Peltio" <peltioNOSP at Miname.com.invalid>
- Sender: owner-wri-mathgroup at wolfram.com
"Bobby Treat" wrote
>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
Also, look at this:
vx1'[4.5]
-0.0267501
vx1'[4.6]
vx1'[4.6]
It seems that the derivative returns a value (whatever it is) for
t<4.5789474 (approximately) and returns unevaluated for values higher than
that (and yet lower than 5). What is it that causes this behaviour? Is it
Condition's fault?
Out of curiosity, why 4.5789474? : )
A plot of the two functions:
Plot[Evaluate[{vx1'[t],vx2'[t]}],{t,4.3,4.65}]
shows that they seem to be 90° out of phase in a 1:2 ratio.
As Polonius once said: "yet there is method in't". : )
cheers,
Peltio
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