• To: mathgroup at smc.vnet.net
• From: sean <sean_incali at yahoo.com>
• Date: Sat, 25 Jul 2009 04:17:30 -0400 (EDT)

```you need more equations or less unknowns. Even then it's unclear what
you're trying to accomplish.

You have specified 4 equations for s'[t], c'[t], p'[t], a'[t]

Yet in your system, you have b2[t], b[t], bp[t] while bp' b' appearing
in the p'[t] equation doesn't make any sense.  Also, you can't just
say [a] and [s] or [c] for that matter. [] is used surround the
argument in this case t.

Seems like you want to solve for b2, s, c, p, b, bp, which requires
you to specify 6 equations total for THOSE variables. Specifying a'[t]
doesn't help you if the variables above are the one you need to obtain
the solutions for.

Also if you specified the initial b[0]== 0.025 then you shouldn't
specify it again as b[0]==0. And since you're solving for the
variables above, you have to specify the initial conditions for those
variables.

Read about NDSolve in the help browser. It gives many good examples.

ClearAll["Global`*"]
des = {s'[t] == -k1f  s[t] b[t] + k1r c[t],
c'[t] == k1f a[t] s[t] - k1r c[t],
p'[t] == k2 c[t],
bp'[t] == k2 c[t],
b'[t] == k2 c[t],
a'[t] == -k1f a[t] s[t] + k1r c[t]};

ics = {s[0] == 0.005, c[0] == 0, b[0] == 0.025, p[0] == 0=
, bp[0] == 0,
a[0] == 0};
var = {s, c, p, b, bp, a};
sol = NDSolve[{des, ics} /. {k1f -> 0.1, k1r -> 0.01, k2 -> 1}, {s, c,
p, b, bp, a}, {t, 0, 1500}]

On Jul 24, 3:10 am, angela <amb... at cornell.edu> wrote:
> mechanism = NDSolve[{
>     s'[t] == -k1f  s[t] b2[t] + k1r c[t],
>     c'[t] == k1f [a] [s] - k1r c[t],
>     p'[t] == k2[c] == bp[t] == b'[t],
>     a'[t] == -k1f a[t] s[t] + k1r c[t],
>     b2'[t] == -k1f s[t] b2[t] + k2f c[t],
>     s[0] == 0.005;
>     b[0] == 0.025;
>     p[0] == 0;
>     bp[0] == 0;
>     b[0] == 0}
>    /. {k1f -> 0.1, k1r -> 0.01, k2 -> 1},
>   {b2, s, c, p, b, bp},
>   {t, 0, 1500}]
>
> NDSolve::deqn: Equation or list of equations expected instead of True \
> in the first argument {s^\[Prime][t]==0.01 c[t]-0.1 b2[t] \
> s[t],<<4>>,True}. >>

```

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