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## System of ODE - part III

 From: Dennis Bayrock Subject: System of ODE - part III Date: Tue, 02 Oct 2001 19:05:34 -0600 User-agent: Mozilla/5.0 (Windows; U; WinNT4.0; en-US; rv:0.9.4) Gecko/20010913

```Hello!

```
I want to thank everyone again in helping me (particularly Przemek Klosowski!) in helping me to understand Octave's syntax. I am very grateful. With some decifering, I have managed to properly enter my own model consisting of a system of differential-algebraic equations into Octave in order for it to integrate the equations. I am happy to report that it works very well! The results with initial test parameters are precisely what was expected!
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Now, is there a way to have Octave determine values for multiple initial constants that are part of my model so that a value from one of the integrated equations can match a specified value? Basically I want to curve fit the resulting plots to my actual experimental data and have Octave determine the best values for the constants that would accomplish this. In the past I have used Excel's SOLVER function to accomplish this task but wish to know if Octave can do the same thing. Again I would humbly ask that someone would give me an actual example that I could enter into Octave so that I can learn by example. As I mentioned before I am not an engineer or a mathematician but would like to learn more about the mathematics in this area of research.
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If a hypothetical example would be of use as a base, then:

function res = f (x, xdot, t)
D=0.02
umax=0.4
res = zeros (3,1);
res(1) = xdot(1) - D*x(1)*x(2)*xdot(3);
res(2) = xdot(2) - umax*x(1)*x(3)*xdot(1);
res(3) = xdot(3) - x(1) - D*xdot(1) - xdot(2);
endfunction

```
x0 = [5,50,0]; xdot0 = [0,0,0];
```
t = linspace (0, 100, 1000);
x = dassl ("f",x0,xdot0,t);
plot (t,x)
pause

```
Dennis Bayrock, P.hD
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