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Re: problem
*To*: mathgroup at smc.vnet.net
*Subject*: [mg100330] Re: [mg100302] problem
*From*: "David Park" <djmpark at comcast.net>
*Date*: Mon, 1 Jun 2009 07:08:02 -0400 (EDT)
*References*: <21606229.1243766725441.JavaMail.root@n11>
Sometimes, in attempting to use DSolve or Solve, it helps to avoid
approximate numbers such as 0.5. So, I rewrote your differential equations
as follows (but it didn't help any with DSolve):
deqns = {y''[x] == -y[x]*((y[x])^2 + (z[x])^2)^(1/2),
z''[x] == -z[x]*((y[x])^2 + (z[x])^2)^(1/2), y'[0] == 1, y[0] == 1,
z'[0] == 1/2, z[0] == 1};
Clear[y, z];
dsols = First@NDSolve[deqns, {y, z}, {x, -100, 100}]
{y[x_], z[x_]} = {y[x], z[x]} /. dsols
ParametricPlot[{y[x], z[x]}, {x, -100, 100},
Frame -> True]
David Park
djmpark at comcast.net
http://home.comcast.net/~djmpark/
From: parmida shabestary [mailto:dj_poni at yahoo.com]
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
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