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MathGroup Archive 2005

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Re: DSolve and K$31, i am puzzled

  • To: mathgroup at smc.vnet.net
  • Subject: [mg57094] Re: [mg57078] DSolve and K$31, i am puzzled
  • From: Chris Chiasson <chris.chiasson at gmail.com>
  • Date: Sun, 15 May 2005 03:03:48 -0400 (EDT)
  • References: <200505140858.EAA09494@smc.vnet.net>
  • Reply-to: Chris Chiasson <chris.chiasson at gmail.com>
  • Sender: owner-wri-mathgroup at wolfram.com

It might be a dummy variable. I have seen it when Mathematica is
evaluating complicated integrals and needs to return the result in
terms of an integral (in the dummy variable).

In other words, the output looked like: Integral[ function of $K2 ,{$K2,a,b}]

By the way, when I evaluated your input, I didn't have the dummy
variable in my output:
{{f[t]->-((p-E^(F1*t)*p1+E^(F2*t)*p2)/
Sqrt[(p-E^(F1*t)*p1+E^(F2*t)*p2)^2])+
((p-E^(F1*t)*p1+E^(F2*t)*p2)*t)/
Sqrt[(p-E^(F1*t)*p1+E^(F2*t)*p2)^2]+C[1]}}

In[73]:=
$Version

Out[73]=
5.0 for Microsoft Windows (November 18, 2003)


On 5/14/05, David Boily <dsboily at fastmail.ca> wrote:
> When i try to solve this differential equation with the command:
> 
> In[1]:= DSolve[f'[t] == Sign[p2 Exp[F2 t] - p1 Exp[F1 t] + p], f[t], t]
> 
> where p, p1, p2, F1 and F2 are constants i get the answer
> 
>                         F1 t       F2 t
>                   (p - E     p1 + E     p2) (-K$31 + t)
> Out[1]= {{f[t] -> ------------------------------------- + C[1]}}
>                                F1 t       F2 t    2
>                     Sqrt[(p - E     p1 + E     p2) ]
> 
> what the hell is K$31? I have tried to find out with google or
> the mathematica 5 online docs but have found nothing.
> 
> can someone enlighten me?
> 
> David Boily
> Centre for Intelligent Machines
> McGill University
> Montreal, Quebec
> 
> 


-- 
Chris Chiasson
http://chrischiasson.com/
1 (810) 265-3161


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