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MathGroup Archive 2007

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Re: Kernel Crashing with NDSolve Command

  • To: mathgroup at smc.vnet.net
  • Subject: [mg73761] Re: Kernel Crashing with NDSolve Command
  • From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
  • Date: Wed, 28 Feb 2007 04:23:43 -0500 (EST)
  • Organization: Uni Leipzig
  • References: <erop18$94d$1@smc.vnet.net>
  • Reply-to: kuska at informatik.uni-leipzig.de

Hi,

have you ever taken a look onto the conditions,
that a numerical solution of an initial value
problem exists ??

There is a propery of the right hand side
called Lipshitz continuous and Min[] will
violate this condition.

Second, you don't need assigment statements
because


NDSolve[
{y'[x]==Min[s[x]+Sin[x],Cos[x]-s[x]],y[0]==0}/.
   s[x]->x^2,
  y,{x,0,3}]

will work
and instead of s[x]->x^2
you may use the output of Solve[]

Regards
   Jens

pradeep wrote:
> Hi all
> i have this rather innocuous looking NDSolve command thats crashing the 
> mathematica kernel,
> NDSolve[{y'[x]==Min[s[x]+Sin[x],Cos[x]-s[x]],y[0]==0,s[x]==x^2},{y,s},{x,0,3}]
> 
> If i were to substitute s[x] in this equation with x^2 and then try 
> solving, i get an answer, if i assign s[x] in advance and try solving 
> it, i still get an answer but the nature of the algorithm followed by 
> NDSolve doesnt allow it to take s[x] as a dependent variable and still 
> have it occur inside the Min function! i find that weird!
> Someone have an explanation??
> thanks in advance!
> Pradeep
> p.s. also note the that the nature of my application is such that i'd 
> like to solve this bunch of equations in a single shot without 
> assignment statements hence i dont have use for the two approaches that 
> i mentioned worked.
> 


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