Re: A question about numerically solving differential equations

*To*: mathgroup at smc.vnet.net*Subject*: [mg130331] Re: A question about numerically solving differential equations*From*: "Kevin J. McCann" <kjm at KevinMcCann.com>*Date*: Wed, 3 Apr 2013 04:10:22 -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> <kjb43b$8jm$1@smc.vnet.net> <kje14v$gv9$1@smc.vnet.net>

In your second DE below, you should type NDSolve, not NDSOlve. Also, your "primes" that indicate derivatives are "back quotes" use the regular single quote (apostrophe): NDSolve[{y'[x] == g[x], g'[x] == g[x] + y[x], g[1] == 1, y[1] == 1}, {y, g}, {x, 1, 2}] As for the first one, I can't say, since you did not post any initial conditions. Cheers, Kevin On 4/2/2013 3:25 AM, debguy 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. >