Re: question ,,thankx!!!

• To: mathgroup at smc.vnet.net
• Subject: [mg70709] Re: [mg70681] question ,,thankx!!!
• From: Bob Hanlon <hanlonr at cox.net>
• Date: Tue, 24 Oct 2006 02:24:11 -0400 (EDT)

```You need to define r at all points in the interval including 0, 100, 110,  200, and 400.

r[t_]:=0/;0<=t<100;
r[t_]:=10/;100<=t<110;
r[t_]:=2.5/;110<=t<200;
r[t_]:=0/;200<=t<=400;

Or more simply

Clear[r];

r[t_]:= Piecewise[{
{10, 100<=t<110},
{2.5, 110<=t<200}}];

sol=NDSolve[{b'[t]==30a'[t],
c'[t]==10a[t](100-c[t])-0.3c[t],
d'[t]==400a[t],
a'[t]+b'[t]+c'[t]+d'[t]\[Equal]r[t],
a[0]==0,b[0]==0,c[0]==0,d[0]==0},
{a[t],b[t],c[t],d[t]},{t,0,400}];

Plot[Evaluate[
{a[t],b[t],c[t],d[t]}/.sol[[1]]],
{t,0,400},
PlotStyle->{Red, Blue, Green,Black},
PlotRange->All,Frame->True,
Axes->False, ImageSize->500];

Plot[Evaluate[
{a[t],b[t],c[t],d[t]}/.sol[[1]]],
{t,0,400},
PlotStyle->{Red, Blue, Green,Black},
PlotRange->{0,0.7},Frame->True,
Axes->False, ImageSize->500];

Plot[Evaluate[
{a[t],b[t],c[t],d[t]}/.sol[[1]]],
{t,0,400},
PlotStyle->{Red, Blue, Green,Black},
PlotRange->{0,0.025},Frame->True,
Axes->False, ImageSize->500];

Table[{t, a[t],b[t],c[t],d[t]}/.sol[[1]]//Chop,
{t,0,400,20}]

Bob Hanlon

---- walkon <fsun81 at mail.ru> wrote:
> hello to everyone!
> here question is:
> input:
> r[t_] := 0 /; (t > 0) && (t < 100)
> r[t_] := 10 /; (t > 100) && (t < 110)
> r[t_] := 2.5 /; (t > 110) && (t < 200)
> r[t_] := 0 /; (t > 200) && (t < 400)
>
> sol = NDSolve[{b'[t] == 30a'[t],
>          c'[t] == 10a[t](100 - c[t]) -0.3c[t],
>          d'[t] ==400a[t],
>          a'[t] + b'[t] + c'[t] + d'[t] == r[t],
>          a[0] == 0, b[0] == 0, c[0] == 0, d[0] == 0}, {a[t], b[t],
> c[t], d[t]}, {t, 0, 400}]
>
> Plot[({a[t], b[t], c[t], d[t]} /. sol[[1]] // Evaluate), {t, 0,400},
> PlotRange -> All, Frame -> True]
>
> who can tell me what 's wrong with the programming?
> and if I input a certain r[t] value like:
> input:
> sol = NDSolve[{b'[t] == 30a'[t], c'[t] == 10a[t](100 - c[t]) -0.3c[t],
> d'[t] ==400a[t], a'[t] + b'[t] + c'[t] + d'[t] == 0, a[0] == 10, b[0]
> == 0, c[0] == 0, d[0] == 0}, {a[t], b[t], c[t], d[t]}, {t, 0, 100}]
> Plot[({a[t], b[t], c[t], d[t]} /. sol[[1]] // Evaluate), {t, 0,100},
> PlotRange -> All, Frame -> True]
> output:
> [Graphic]
> It works well!
> so,,whether the programming can only be seperately resolved or not?
>
> the most important is that I need to get the numerical value of
> a[t],b[t],c[t],d[t]
> at each time point(0-400),but how to list them from the result of
> NDSolve??even I can show the picture.
>
> thank you very much!!!
>

--

Bob Hanlon
hanlonr at cox.net

```

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