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MathGroup Archive 2004

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DSolve change in v5 -- undocumented error message

  • To: mathgroup at smc.vnet.net
  • Subject: [mg46751] DSolve change in v5 -- undocumented error message
  • From: Gareth Russell <gjr2008 at columbia.edu>
  • Date: Fri, 5 Mar 2004 01:47:08 -0500 (EST)
  • Organization: Columbia University
  • Sender: owner-wri-mathgroup at wolfram.com

Hi,

The following expression used to work in v4:

DSolve[{n'[t] == r*n[t]*(1 - n[t]/k), n[0] == n0}, n[t], t]

In v5, I get the message

"DSolve::bvfail: For some branches of the general solution, unable to 
solve the conditions."

Clicking on the "More" link takes me to a page in the Help Browser with 
"Notes for this message have not yet been added."

Interestingly, the expression without initial conditions works just 
like before

In[31]:=
DSolve[{n'[t] == r*n[t]*(1 - n[t]/k)}, n[t], t]

Out[31]=
\!\({{n[t] \[Rule] \(\[ExponentialE]\^\(r\ t + k\ C[1]\)\ k\)\/\(\(-1\) 
+ \
\[ExponentialE]\^\(r\ t + k\ C[1]\)\)}}\)

Does anyone know what is being done differently in v5. And more 
practically, is there a way to recover v4's ability to get a solution. 
Perhaps with assumptions?

Many thanks,

Gareth Russell
Columbia University


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