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## moving from matlab to octave

**From**: |
Jeff Sadowski |

**Subject**: |
moving from matlab to octave |

**Date**: |
Fri, 21 Feb 2003 12:46:08 -0700 (MST) |

I am new to using these applications and I really
don't understand exactly what I'm doing in either.
I have a matlab project that looks like this.
file vdpol.m contains
function xdot=vdpol(t,x)
beta=5.0;
omega=1.5;
xdot=[x(2);x(2).*(1-x(1)*x(1))-x(1) + beta*cos(x(3));omega];
supposidly this means
dx_sub1/dt=x_sub2
dx_sub2/dt=x_sub2((1-x_sub1)^2)-x_sub1+beta*cos(x_sub3)
dx_sub3/dt=omega
then I enter matlab and run this
tspan=[0,20]
x0=[1.0,0.0,2.0];
[t,x]=ode45('vdpol',tspan,x0);
x1=x(:,1)
plot(t,x1)
when I try it in octavelike this
tspan=[0,20]
x0=[1.0,0.0,2.0];
[t,x]=lsode('vdpol',tspan,x0);
I get the improper usage of lsode message
if I try
y=lsode('vdpol',tspan,x0);
I get
error: invalid vector index = 2
error: evaluating index expression near line 4, column 9
error: evaluating assignment expression near line 4, column 6
error: called from `vdpol' in file `/home/guest/math316/vdpol.m'
error: lsode: evaluation of user-supplied function failed
error: lsode: inconsistent sizes for state and derivative vectors
I'm not sure what this even means any help would be greatly appriciated.
If I could get through the ode part I'm sure the other two will work
I've worked with octave in my linear algabra class and from that point
on matlab and octave seemed very simalar
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**moving from matlab to octave**,
*Jeff Sadowski* **<=**