Re: DSolve change in v5 -- undocumented error message

*To*: mathgroup at smc.vnet.net*Subject*: [mg46762] Re: DSolve change in v5 -- undocumented error message*From*: bobhanlon at aol.com (Bob Hanlon)*Date*: Sun, 7 Mar 2004 01:33:40 -0500 (EST)*References*: <c298r9$56c$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

eqn=n'[t]==r*n[t]*(1-n[t]/k); ans1 =DSolve[eqn,n[t],t][[1]]; Off[Solve::ifun]; ans2 = ans1 /. Solve[(n[0] /. (ans1 /. t->0))==n0, C[1]][[1]] // Simplify {n[t] -> (E^(r*t)*k*n0)/ (k + (-1 + E^(r*t))*n0)} ans2 /. t->0 {n[0] -> n0} eqn /.Join[ans2, D[ans2, t]//Simplify]// Simplify True Bob Hanlon In article <c298r9$56c$1 at smc.vnet.net>, Gareth Russell <gjr2008 at columbia.edu> wrote: << 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?