
Re: Incredible slow Plot
Posted:
Jul 12, 2011 6:09 AM


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@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@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@yahoo.com >

