Re: Solving ODE

[LUK ShunTim]

fraud profile wrote:
> Hi,
> 
> I am using lsode to solve a simple ODE on Octave 2.1.72. <http://2.1.72.>
> The ode is:
> Solve: y''(t) + y(t) =0
> such that:
> y(0)=3 & y(pi/2)=3
> 
> My code for this is:
> 
> -------- file f.m ---------
> function xdot = f (x, t)
>   xdot = zeros (2,1);
> 
>   xdot(1) =  x(2);
>   xdot(2) =  -x(1);
> endfunction
> ---- end of f.m -----
> 
> -------- file ode.m ---------
>  l = linspace (0, pi/2, 20);
> 
> y_min=[3;3];
>     psi = lsode( "f", y_min, l );
>  
> plot(l,psi(:,1));
> ---- end of ode.m -----
> 
> I am getting correct answer with this. But lsode requires y_min which is
> actually the value of x(1) and x(2) at t=0. I have the value of x(1) at
> t=0 and t=pi/2.(I got the value of x(2) at t=0 by solving this on Matlab
> and then solved this by adding y_min=[3;3]; here). How can I use the
> given boundary conditions so that I don't need the values of x(2) to
> solve the problem.
> 
> Thank you
> 

Hello,

Maybe be you can google for "shooting method" if you want to use lsode
or other initial value problem solvers for a boundary value problem.

Alternatively, you can try the odebvp package from octave-forge.

Regards,
ST
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