MATLAB Central Newsreader - using global variable in equation used by ODE solver

using global variable in equation used by ODE solver

Tariq — Tue, 03 Nov 2009 18:35:04 -0500

i have problem in my program
i created one variable 'v' in main file , the value of that variable is used in the equation in other program as global variable.

when i run main program having ode45 solver for that equation having variable 'v' it gives error
??? Error using ==> odearguments at 117
Solving EGG2 requires an initial condition vector of length 1.
can any body guide me about this.

is there is way to use value of one variable in other function (equation) which will be solved through ODE solver.
my code is

main program
--------------------
clc;
clear all;
global v;
x=[-1;1];
v= 2*x;
[x,y]= ode45(@eg,[-1 1],[0.1],v);
plot (x,y);
--------------
function dy =eg(x,y)
global v;
dy= -v*y + x;
end

Re: using global variable in equation used by ODE solver

Nasser M. Abbasi — Tue, 03 Nov 2009 23:04:54 -0500

"Tariq " <t.umer@lancaster.ac.uk> wrote in message
news:hcpt4o$n8b$1@fred.mathworks.com...
>i have problem in my program
> i created one variable 'v' in main file , the value of that variable is
> used in the equation in other program as global variable.
>
> when i run main program having ode45 solver for that equation having
> variable 'v' it gives error
> ??? Error using ==> odearguments at 117
> Solving EGG2 requires an initial condition vector of length 1.
> can any body guide me about this.
>
> is there is way to use value of one variable in other function (equation)
> which will be solved through ODE solver.
> my code is
>
> main program
> --------------------
> clc;
> clear all;
> global v;
> x=[-1;1];
> v= 2*x;
> [x,y]= ode45(@eg,[-1 1],[0.1],v);
> plot (x,y);
> --------------
> function dy =eg(x,y)
> global v;
> dy= -v*y + x;
> end

The problem is in your eg function.
When you type "v*y", notice that v is a vector of length 2, so this causes
dy to become a vector of length 2, hence the problem.

I do not know what you are doing here. And why you are passing 'v' to ode45
since it is allready global. try v scalar, and try this

v= 99;
[x,y]= ode45(@eg,[-1 1],[0.1]);

--Nasser

Re: using global variable in equation used by ODE solver

Tariq — Fri, 06 Nov 2009 14:06:03 -0500

hello dear,
thanks for you response , i have checked the error ,
it is ok, how i can get specific value of v from the vector having different values of v to be used in the equation in eg (eq for ode solver).

"Nasser M. Abbasi" <nma@12000.org> wrote in message <qG2Im.43$gg6.15@newsfe25.iad>...
>
> "Tariq " <t.umer@lancaster.ac.uk> wrote in message
> news:hcpt4o$n8b$1@fred.mathworks.com...
> >i have problem in my program
> > i created one variable 'v' in main file , the value of that variable is
> > used in the equation in other program as global variable.
> >
> > when i run main program having ode45 solver for that equation having
> > variable 'v' it gives error
> > ??? Error using ==> odearguments at 117
> > Solving EGG2 requires an initial condition vector of length 1.
> > can any body guide me about this.
> >
> > is there is way to use value of one variable in other function (equation)
> > which will be solved through ODE solver.
> > my code is
> >
> > main program
> > --------------------
> > clc;
> > clear all;
> > global v;
> > x=[-1;1];
> > v= 2*x;
> > [x,y]= ode45(@eg,[-1 1],[0.1],v);
> > plot (x,y);
> > --------------
> > function dy =eg(x,y)
> > global v;
> > dy= -v*y + x;
> > end
>
> The problem is in your eg function.
> When you type "v*y", notice that v is a vector of length 2, so this causes
> dy to become a vector of length 2, hence the problem.
>
> I do not know what you are doing here. And why you are passing 'v' to ode45
> since it is allready global. try v scalar, and try this
>
> v= 99;
> [x,y]= ode45(@eg,[-1 1],[0.1]);
>
> --Nasser
>
>