Mathematica 9 is now available
Services & Resources / Wolfram Forums / MathGroup Archive
-----

MathGroup Archive 2009

[Date Index] [Thread Index] [Author Index]

Search the Archive

Re: Problem with DSolve

  • To: mathgroup at smc.vnet.net
  • Subject: [mg96461] Re: [mg96410] Problem with DSolve
  • From: "David Park" <djmpark at comcast.net>
  • Date: Sat, 14 Feb 2009 03:08:10 -0500 (EST)
  • References: <8204467.1234516287118.JavaMail.root@m02>

Try an exact version of the equations. You still obtain a warning about
inverse functions, but you do obtain a solution.

Clear[y];
First@DSolve[{y'[x] == y[x]/50 - y[x]^2, y[0] == a}, y, x];
y[x_] = y[x] /. %
{y'[x] == y[x]/50 - y[x]^2, y[0] == a}

(a E^(x/50))/(1 - 50 a + 50 a E^(x/50))
{True, True}


David Park
djmpark at comcast.net
http://home.comcast.net/~djmpark/  


From: Tony [mailto:aezajac at optonline.net] 

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.
>>




  • Prev by Date: Re: Chain Matrix
  • Next by Date: Re: Chain Matrix
  • Previous by thread: Re: Problem with DSolve
  • Next by thread: Re: Problem with DSolve