Re: Can't take a value from an InterpolatingFunction.

*To*: mathgroup at smc.vnet.net*Subject*: [mg13638] Re: Can't take a value from an InterpolatingFunction.*From*: "Allan Hayes" <hay at haystack.demon.cc.uk>*Date*: Fri, 7 Aug 1998 09:14:05 +0100*References*: <6qbqv3$a71@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

John: The following may be relevant Table[First[y[100] /. NDSolve[{x'[t] == y[t], y'[t] == -0.01*y[t] - Sin[x[t]], x[0] == 0, y[0] == y0}, {x, y}, {t, 0, 100}, MaxSteps -> 3000]], {y0, 2, 2.5, 0.1}] {-0.594081,0.438559,1.46045,1.21722,0.449353,-0.834324} Allan ------------------------------------------------------------- Allan Hayes Training and Consulting Leicester UK http://www.haystack.demon.co.uk hay at haystack.demon.co.uk voice: +44 (0)116 271 4198 fax: +44(0)116 271 8642 *************** I. Ioannou wrote in message <6qbqv3$a71 at smc.vnet.net>... >Hi all, > >I've set up and solved a system of two differential equations, according >to the following prescription; > > solution = > NDSolve[{r'[t] == .....equation1......, > p'[t] == .....equation2......, > r[0] == 0.,p[0] == p0}, {r, p}, {t, 0, 0.2}, > MaxSteps \[Rule] 300000, Method \[Rule] Automatic] > >All has worked very nicely. However, I need now to take the value of r >at t=0.2 and I can't seem to be able to do it. > >I should point out that the Book suggestion r[0.2] /. % doesn't work, >because the above statement is within a For loop and is run many times. >(to collect various r[0.2] values that come out) So, it's within one >big cell. > >The error reported sais that solution is not a valid lookup table. Well, >from what I understand, it's a set (?) of two InterpolatingFunctions. >If I knew what kind of entity solution is, I might be able to figure >how to instruct Mathematica to let me access r[0.2]. > >Any help appreciated, thanks, John > >-- > Ioannis I Ioannou phone: (206)-543-1372 > g-2 group, Atomic Physics fax: (206)-685-0635 > Department of Physics > University of Washington e-mail: iioannou at u.washington.edu >