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Re: A question about numerically solving differential equations

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  • 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)
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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.
>



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