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## lsode

 From: Sigfrid Lundberg Subject: lsode Date: Thu, 24 Jun 93 22:18 MET DST

```I'm a newbie octave user. Everything seem to work as expected, but there
is one I don't understand. I have written a tiny function:

function xdot = volterra ( x , t)

#
#  Integrate lotka-volterra
#
global x xdot;

r = 0.25;
k = 1.4;
a=1.5;
b=0.16;
c=0.9;
d=0.8;

xdot (1) = r*x (1) * (1 - x (1)/k) - a*x (1)*x (2)/(1+b*x (1));
xdot (2) = c*a*x (1)*x (2)/(1+b*x (1))-d*x (2);

endfunction

Then I start octave, and load this function:

Octave, version 0.72.  Copyright (C) 1992, 1993, John W. Eaton.
This is free software with ABSOLUTELY NO WARRANTY.
For details, type `warranty'.

octave:1> eval("volterra");
error: `x' undefined

octave:2> x=[1;6]
x =

12
6

I can evaluate this function

octave:4> volterra(x,5)
ans =

-59.701
28.488

But, if I try to use lsode for solving this predator-prey model

octave:18> x=[1;6]
x =

1
6

octave:19> lsode ('volterra',x,30,0.01)
ans =

1  6

nothing interesting happens. What am I doing wrong?

Regards,

Sigfrid

```

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