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MathGroup Archive 2006

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Re: differential equation solve

  • To: mathgroup at smc.vnet.net
  • Subject: [mg68847] Re: [mg68821] differential equation solve
  • From: Bob Hanlon <hanlonr at cox.net>
  • Date: Mon, 21 Aug 2006 03:27:46 -0400 (EDT)
  • Reply-to: hanlonr at cox.net
  • Sender: owner-wri-mathgroup at wolfram.com

Make sure that all of your variables are clear

$Version

5.2 for Mac OS X (June 20, 2005)

Clear[x,y,t];

DSolve[{y'[x] == r*y[x], y[0] == a}, y, x]

{{y -> Function[{x}, a*E^(r*x)]}}

DSolve[{y'[x] == r*y[x], y[0] == a}, y[x], x]

{{y[x] -> a*E^(r*x)}}

Off[Solve::ifun];

DSolve[{x'[t] == r*x[t]*(1 - x[t]/xm), x[0] == x0}, x, t]

{{x -> Function[{t}, (E^(r*t)*x0*xm)/(E^(r*t)*x0 - x0 + xm)]}}

DSolve[{x'[t] == r*x[t]*(1 - x[t]/xm), x[0] == x0}, x[t], t]

{{x[t] -> (E^(r*t)*x0*xm)/(E^(r*t)*x0 - x0 + xm)}}


Bob Hanlon

---- elvis <rapstone at gmail.com> wrote: 
> Here we often use mathematica to solve differential equations, when I
> encouter a equation with several constrains I set them to those values.
> But it cannot solve it and have the following warnings:
> 
>     DSolve::deqx: Supplied equations are not differential equations of
> the given functions.
> 
> Give a very simple differential equation here:
> 
>   DSolve[{y'[x] == r*y[x], y[0] == a}, y, x]
> 
> another equation:
> 
> \!\(DSolve[{\(x'\)[t] == r*x[t] \((1 - x[t]\/xm)\), x[0] == x0}, x,
> t]\)
> 
> this face anothe prolbem
> 
> Can anyone help to "solve" this problem for me?
> Thanks!
> 


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