Re: Incredible slow Plot

*To*: mathgroup at smc.vnet.net*Subject*: [mg120184] Re: Incredible slow Plot*From*: Iván Lazaro <gaminster at gmail.com>*Date*: Tue, 12 Jul 2011 06:58:18 -0400 (EDT)*References*: <iv9etb$dg1$1@smc.vnet.net>

Well, i'm going to try to clarify it a little, but, as I said, is not posible to paste the complete code; the equations are just too big. I also made a mistake writing the last email. So, for example, {eqns, cond}={f1'[t]==a11*f1[t]+a12*f2[t]+...+a1N*fN[t],..., fN'[t]==aN1*f1[t]+aN2*f2[t]+...+aNN*fN[t], f1[0]==t01,...,fN[0]==t0N}, and f={f1,f2,...,fN}. If Something is, say 1, then sol[[1, 1]]: f1[t]->InterpolatingFunction[{{0.`,1200.`}},"<>"][t] and sol[[1, 1, 2]] is just InterpolatingFunction[{{0.`,1200.`}},"<>"][t]. So, with sol=NDSolve[{eqns, cond},f,{t,0,1200}][[1]]; a[t_]=sol[[1, 1, 2]] b[t_]=sol[[1, 2, 2]] i'm just extracting the solution for two of my variables, f1 and f2. Plot "a" and "b", Plot[{a[t], b[t]},{t,0,1200}], was fast; however this: Plot[{Evaluate[f1[t]/.sol], Evaluate[f2[t]/.sol]},{t,0,1200}], was, somehow, imposible. 2011/7/11 DrMajorBob <btreat1 at austin.rr.com>: >> and that was it. However I don't understand this. Was the problem the >> "size" and "amount" of interpolated functions? > > I don't understand it either. The two methods seem equivalent, but this code > >> sol=NDSolve[{eqns, cond},f,{t,0,1200}][[1]]; >> a=sol[[1, Something, 2]] >> b=sol[[1, Something+1, 2]] > > suggests that you're solving for one function f in the first line, and YET, > you're extracting two solutions a and b in the next two lines. That's not > possible, so you're not showing us the code you actually used. (We know that > anyway, since "eqns", "cond", and "Something" are undefined.) > > I suspect in the real code, the two methods that seem equivalent are NOT > equivalent at all. > > Bobby > > On Mon, 11 Jul 2011 05:58:03 -0500, Iv=E1n Lazaro <gaminster at gmail.com> wrote: > >> Hi! >> >> Yes, I tried >> >> sol=NDSolve[{eqns, cond},f,{t,0,1200}][[1]]; >> Plot[Evaluate[f[t]/.sol],{t,0,1200}], >> >> but that was a pain. Thanks to Bobby I managed to solve my speed problem: >> >> Instead of >> >> sol=NDSolve[{eqns, cond},f,{t,0,1200}][[1]]; >> Plot[Evaluate[f[t]/.sol],{t,0,1200}], >> >> I selected the specific solutions I needed, and Set them to a variable >> that then I plot: >> >> >> >> sol=NDSolve[{eqns, cond},f,{t,0,1200}][[1]]; >> a=sol[[1, Something, 2]] >> b=sol[[1, Something+1, 2]] >> >> Plot[{a[t],b[t]}],{t,0,1200}], >> >> and that was it. However I don't understand this. Was the problem the >> "size" and "amount" of interpolated functions? >> > > > -- > DrMajorBob at yahoo.com >