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MathGroup Archive 2002

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Re: Step Info from NDSolve

  • To: mathgroup at smc.vnet.net
  • Subject: [mg33648] Re: Step Info from NDSolve
  • From: "Allan Hayes" <hay at haystack.demon.co.uk>
  • Date: Thu, 4 Apr 2002 19:40:14 -0500 (EST)
  • References: <a8g34f$b2p$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

"Brian Higgins" <bghiggins at ucdavis.edu> wrote in message
news:a8g34f$b2p$1 at smc.vnet.net...
> Hi Mathgroup,
>  Is there anyway to get step information (number of steps, step size)
> from NDSolve during the actual integration

Brian,

The following trick is generally applicable:

If a print out of progress is sufficient,

    h[(x_)?NumberQ, fx_, rhs_] := (Print[{x, fx}]; rhs)


    NDSolve[{f'[x] == h[x, f[x], 2*f[x]],  f[0] == 1}, f, {x,0, 1}]

If you want data to work on then

    g[(x_)?NumberQ, fx_, rhs_] :=  (points = Append[points, {x, fx}]; rhs)

    points = {};
    NDSolve[{f'[x] == g[x, f[x], 2*f[x]],  f[0] == 1}, f, {x, 0, 1}]


--
Allan

---------------------
Allan Hayes
Mathematica Training and Consulting
Leicester UK
www.haystack.demon.co.uk
hay at haystack.demon.co.uk
Voice: +44 (0)116 271 4198
Fax: +44 (0)870 164 0565










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