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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.
>>
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