Re: what went wrong in this ordinary differential eq
- To: mathgroup at smc.vnet.net
- Subject: [mg98544] Re: [mg98504] what went wrong in this ordinary differential eq
- From: DrMajorBob <btreat1 at austin.rr.com>
- Date: Sun, 12 Apr 2009 03:47:37 -0400 (EDT)
- References: <200904110754.DAA22155@smc.vnet.net>
- Reply-to: drmajorbob at bigfoot.com
g[x_]:=x y'[x]
s=NDSolve[{g'[x]+Sin[y[x]]*y[x]==0,y[0]==1,y'[0]==0},y[x],{x,0,30}]
Power::infy: Infinite expression 1/0. encountered. >>
NDSolve::ndnum: Encountered non-numerical value for a derivative at x ==
0.`. >>
NDSolve[{Sin[y[x]] y[x]+(y^\[Prime])[x]+x
(y^\[Prime]\[Prime])[x]==0,y[0]==1,(y^\[Prime])[0]==0},y[x],{x,0,30}]
Mathematica needs to solve for y''[0] and can't, because its coefficient
(x) is 0.
THIS problem works fine, on the other hand:
Clear[s]
g[x_]:=(x+1) y'[x]
s[x_]=y[x]/.NDSolve[{g'[x]+Sin[y[x]]*y[x]==0,y[0]==1,y'[0]==0},y[x],{x,0,30}]
{InterpolatingFunction[{{0.,30.}},<>][x]}
Plot[s@x, {x, 0, 30}, PlotStyle -> Automatic]
Bobby
On Sat, 11 Apr 2009 02:54:57 -0500, Janpou Nee <jpnee2000 at yahoo.com.tw>
wrote:
> s = NDSolve[{(x*y'[x])'[x] + Sin[y[x]]*y[x] == 0, y[0] == 1,
> y'[0] == 0}, y[x], {x, 0, 30}];
> Plot[Evaluate[{y[x]} /. s], {x, 0, 30}, PlotStyle -> Automatic]
>
--
DrMajorBob at bigfoot.com