Re: Re: How to get data from solvin'

*To*: mathgroup at smc.vnet.net*Subject*: [mg104816] Re: [mg104143] Re: [mg104128] How to get data from solvin'*From*: DrMajorBob <btreat1 at austin.rr.com>*Date*: Tue, 10 Nov 2009 06:03:56 -0500 (EST)*References*: <200910200852.EAA06192@smc.vnet.net>*Reply-to*: drmajorbob at yahoo.com

For instance: Needs["DifferentialEquations`InterpolatingFunctionAnatomy`"] Clear[y] s = y /. First@ NDSolve[{y'[x] == y[x] Cos[x + y[x]], y[0] == 1}, y, {x, 0, 30}]; pts1 = {#, s@#} & /@ First@InterpolatingFunctionCoordinates@s; ListPlot@pts You could also do it in reverse, so to speak, without the extender package: Clear[y] s = y /. First@ NDSolve[{y'[x] == y[x] Cos[x + y[x]], y[0] == 1}, y, {x, 0, 30}]; p = Plot[s@x, {x, 0, 30}, PlotRange -> All]; pts2 = First@Cases[p, Line[points_] :> points, Infinity]; That's a larger set of points, however: Length /@ {pts1, pts2} {339, 1281} Here's the maximum error at the original points: s'[#] - s[#] Cos[# + s[#]] & /@ pts1[[All, 1]] // Abs // Max 1.61028*10^-8 and here's an error computation for the plotted function: s2 = Interpolation@pts2; s2'[#] - s2[#] Cos[# + s2[#]] & /@ pts2[[All, 1]] // Abs // Max 0.000330339 Bobby On Wed, 21 Oct 2009 05:28:23 -0500, Scot Martin <smartin at seas.harvard.edu> wrote: > Yes, there are some features in an extender package. In help file, use > "tutorial/NDSolvePackages" and then start reading there. > > > -----Original Message----- > From: =D0=9C=D0=B8=D1=85=D0=B0=D0=B8=D0=BB = > =D0=A8=D0=B0=D0=BB=D0=B0=D0=B3=D0=B8=D0=BD=D0=BE=D0=B2 = > [mailto:shalm89 at gmail.com] > Sent: Tuesday, October 20, 2009 04:53 > To: mathgroup at smc.vnet.net > Subject: [mg104143] [mg104128] How to get data from solvin' numerically = > differential equation? > > Hi, > Mathematica solves numerically differential equation and makes > interpolation. I can plot this interpolating function. Can I save all > the points in a file or somehow get this data? > Best regards, Mikhail Shalaginov. > > > -- DrMajorBob at yahoo.com