       • To: mathgroup at smc.vnet.net
• Subject: [mg120337] Question about adding events to ndsolve
• From: Chrisantha Fernando <ctf20 at sussex.ac.uk>
• Date: Tue, 19 Jul 2011 06:57:30 -0400 (EDT)

```Please help with adding events to ndsolve. I need to change the
concentrations discretely at certain points in time.

s = NDSolve[{Derivative[X0][t] == 0, Derivative[X1][t] ==
0,
Derivative[X3][t] ==
6.088416` X1[t] X4[t] - 0.000723` X3[t] X4[t] + 7.721115` X1[t]
X7[t] -
9.366268` X3[t] X8[t],
Derivative[X4][t] == -30.` X0[t] X4[t] + 0.031364` X7[t]
X8[t],
Derivative[X7][t] ==
30.` X0[t] X4[t] - 7.721115` X1[t] X7[t] + 9.366268` X3[t] X8[t] -

0.031364` X7[t] X8[t],
Derivative[X8][t] ==
30.` X0[t] X4[t] + 7.721115` X1[t] X7[t] - 9.366268` X3[t] X8[t] -

0.031364` X7[t] X8[t], X0 == 0.`, X1 == 0.`, X3 ==
1,
X4 == 1, X7 == 1, X8 == 1}, {X0, X1, X3, X4, X7,
X8}, {t, 0, 30}]
Plot[Evaluate[{X1[x], X2[x],  X3[x],  X4[x],  X7[x],  X8[x]} /. s], {x,
0,
30}, PlotRange -> All]

and I'd like to add events such that at specific points in time I can
change the values of the variables (chemicals) to a value that I set
externally, i.e. these will be external stimuli to the ODEs that change
the concentrations of chemicals discretely.

Cheers,
Chrisantha

```

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