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Re: What's DSolve's output when it cant find a solution ?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg87205] Re: What's DSolve's output when it cant find a solution ?
  • From: Szabolcs Horvát <szhorvat at gmail.com>
  • Date: Fri, 4 Apr 2008 02:56:57 -0500 (EST)
  • Organization: University of Bergen
  • References: <ft2anu$paq$1@smc.vnet.net>

zerodynamics at gmail.com wrote:
> Im using Mathematica 6 to look for solutions to a system of nonlinear ODE's. I
> don't
> expect a solution, but the only output Im getting is an exact reprint
> of my input.
> This usually means that the arguments to the function are incorrect,
> but Im
> fairly certain they're OK.
> 
> Here is my input:
> 
> In[11]:=   Dsolve[{s''[t] + Cot[u[t]/2]*s'[t]*u'[t] ==  0,   u''[t] -
> Sin[u[t]]*s'[t]^2 == 0 }, {s[t], u[t]}, t]
> Out[11]:= Dsolve[{s''[t] + Cot[u[t]/2]*s'[t]*u'[t] ==  0,   u''[t] -
> Sin[u[t]]*s'[t]^2 == 0 }, {s[t], u[t]}, t]
> 
> Is this what I should expect when DSolve can't find a solution ? Also,
> this is returned immediately
> without any "Running ... ".

Yes, when DSolve returns unevaluated, it cannot solve the equation.  You 
misspelled DSolve as Dsolve above, but Mathematica still cannot solve 
this equation.


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