Re: A question about numerically solving differential equations

*To*: mathgroup at smc.vnet.net*Subject*: [mg130328] Re: A question about numerically solving differential equations*From*: Bob Hanlon <hanlonr357 at gmail.com>*Date*: Wed, 3 Apr 2013 04:09:22 -0400 (EDT)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*Delivered-to*: l-mathgroup@wolfram.com*Delivered-to*: mathgroup-newout@smc.vnet.net*Delivered-to*: mathgroup-newsend@smc.vnet.net*References*: <kirks3$at8$1@smc.vnet.net>

a has to have a numeric value Manipulate[ Plot[ Evaluate[{ Tooltip[f0[r], "f0"], Tooltip[f1[r], "f1"]} /. NDSolve[{ 2 f0'[r]/r + f0''[r] == -2 a f1[r]/r^4 + 2 a f1'[r]/r^3, -2 f1[r]/r^2 + 2 f1'[r]/r + f1''[r] == 2 a f0'[r]/r^3, f0[1] == 1, f1[1] == 1, f0[2] == 1, f1[2] == 1}, {f0[r], f1[r]}, {r, 1, 2}]], {r, 1, 2}, PlotRange -> {0.6, 1.4}], {a, -10, 10, Appearance -> "Labeled"}] Bob Hanlon On Tue, Apr 2, 2013 at 3:26 AM, debguy <johnandsara2 at cox.net> wrote: > 2 D[f0[r], r]/r + D[f0[r], r, r] == -2 A f1[r]/r^4 + 2 A D[f1[r], r]/ > r^3 > -2 f1[r]/r^2 + 2 D[f1[r], r]/r + D[f1[r], r, r] == 2 A D[f0[r], r]/ > r^3 > > I tried it later. I cannot get anything > y`[x]==g`[x]==y[x]==g[x] > to work using any conditions i try. > > NDSOlve[{ y`[x]==g[x], g`[x]==g[x]+y[x], g[1]=1, y[1]=1 },{y,g},{x, > 1,2} ] (* foo *) > > Is the only form I can get to work using two funs. Which is what the > book example uses. > > I'm unsure how to re-express your eq'n that way to try it. > >