MathGroup Archive 2009

[Date Index] [Thread Index] [Author Index]

Search the Archive

Re: problem

  • To: mathgroup at
  • Subject: [mg100346] Re: problem
  • From: "Sjoerd C. de Vries" <sjoerd.c.devries at>
  • Date: Mon, 1 Jun 2009 07:11:00 -0400 (EDT)
  • References: <gvtmio$gic$>

Hi Parmida,

If you examine your two equations you see that they are actually
identical. If you swap z and y you get the same equations.
Conclusion:the solutions for z and y must be the same either. y[x]==z

You can therefore replace z in the first equation with y and solve for
y only.

DSolve[y''[x] == -y[x] Sqrt[(y[x]^2)]*Sqrt[2], y[x], x]

It is still a difficult nut to crack though. Mathematica finds a
result in the form of an integral equation, which doesn't help you

Cheers -- Sjoerd

On May 31, 12:36 pm, parmida shabestary <dj_p... at> wrote:
> Hi
> I'm having trouble solving this set of equations:
> y''[x] =-y[x]*((y[x])^2 + (z[x])^2)^0.5
> z''[x] =-z[x]*((y[x])^2 + (z[x])^2)^0.5
> I couldn't write a DSolve order for it but here is the numerical code I wrote:
> NDSolve[{y''[x] == -y[x]*((y[x])^2 + (z[x])^2)^0.5,
>   z''[x] == -z[x]*((y[x])^2 + (z[x])^2)^0.5, y'[0] == 0.5, z[0]=
 == 1,
>   y[0] == 1, z'[0] == 0.5}, {y, z}, {x, -100, 100}]
> I can plot this answer but what I really need is the parametric solution(a set of equations for z and y depending on x).
> Please help me find the answer.
> thanx
> parmida

  • Prev by Date: Re: Stopping NDSolve after a condition is met x times
  • Next by Date: Re: problem
  • Previous by thread: Re: Stopping NDSolve after a condition is met x times
  • Next by thread: Re: problem