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