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Re: Problem with DSolve

  • To: mathgroup at smc.vnet.net
  • Subject: [mg96465] Re: Problem with DSolve
  • From: Peter Breitfeld <phbrf at t-online.de>
  • Date: Sat, 14 Feb 2009 03:08:54 -0500 (EST)
  • References: <gn3bnf$pt9$1@smc.vnet.net>

Tony wrote:

> can anyone help what is wrong?
> On version 7 I enter
>
>    DSolve[{y'[x]==.02*y[x]-y[x]^2,y[0]==a},y[x],x]
>
> and get
>

> During evaluation of In[58]:= Solve::ifun: Inverse functions are being
> used by Solve, so some solutions may not be found; use Reduce for
> complete solution information. >>

> During evaluation of In[58]:= Solve::ifun: Inverse functions are being
> used by Solve, so some solutions may not be found; use Reduce for
> complete solution information. >>

> During evaluation of In[58]:= DSolve::bvnul: For some branches of the
> general solution, the given boundary conditions lead to an empty
> solution. >>
>

If you avoid using Reals you will still get the warning Solve::ifun, but
not {} as result 


DSolve[{y'[x] == 1/5*y[x] - y[x]^2, y[0] == a}, y[x], x]
                 ^^^
                 
During evaluation of In[29]:= Solve::ifun: Inverse functions are being
used by Solve, so some solutions may not be found; use Reduce for
complete solution information. >>

Out[29]= {{y[x] -> (a E^(x/5))/(1 - 5 a + 5 a E^(x/5))}}

GruÃ? Peter 
-- 
_________________________________________________________
Peter Breitfeld, Bad Saulgau --- http://www.pBreitfeld.de


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