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Re: Problem with DSolve

  • To: mathgroup at smc.vnet.net
  • Subject: [mg96467] Re: [mg96410] Problem with DSolve
  • From: Bob Hanlon <hanlonr at cox.net>
  • Date: Sat, 14 Feb 2009 03:09:16 -0500 (EST)
  • Reply-to: hanlonr at cox.net

Use exact numbers

Off[Solve::ifun]

soln = DSolve[{y'[x] == 2/100*y[x] - y[x]^2, y[0] == a}, y[x], x][[1]]

{y(x)->(a E^(x/50))/(50 a E^(x/50)-50 a+1)}

soln /. x -> 0

{y(0)->a}

y'[x] == 2/100*y[x] - y[x]^2 /. NestList[D[#, x] &, soln[[1]], 1]

True


Bob Hanlon

---- Tony <aezajac at optonline.net> 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. >>




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