ODE45, use ode45 iteratively

Hi, I have the equation m.(xdbldot)+c.(xdot)+k.x = A.w^2; for which obtained the solution through ODE45 using state space form; function ydot=diffeqn(t,y) w=50;m=2;k=500;d=16; ydot(1)=y(2); ydot(2)=-d/m*y(2)-k/m*y(1)+A*w^2; ydot=ydot(:);

followed by

tspan=0:0.001:5;
[t,y]=ode45(@diffeqn,tspan,[0 0]);
yy1=y(:,1);
yy2=y(:,2);
acc=diff(yy2/(t(2)-t(1)));

Now i try to solve the ode for different values of the right side variable 'w'. I tried to use functions,but as ODE45 is inbuilt source code, i could not edit it. Is there any other means of doing it. note: I have also tried Rungekutta 4th order code without using ode45, yet ode45 seems to give finer results.

Thanks, Shravan.

Answer 1

[Friedrich]

Hi,

try using a different function handle

[t,y]=ode45(@(x,t) diffeqn(x,t,w),tspan,[0 0]);

where w is defined before the ODE45 call. In addition change the diffeqn function signature to

function [...] = diffeqn(x,t,w)

So an easy overall example would be (we are looking for the function f = w*x) (so we dont need t and x in our function, since f' = w)

function out = diffeqn( x,t,w )

out = w;

end

We call it with different w and plot it:

w = 2
[t,y]=ode45(@(x,t) diffeqn(x,t,w),[0,5],0);
plot(t,y)
hold on
w = 4
[t,y]=ode45(@(x,t) diffeqn(x,t,w),[0,5],0);
plot(t,y,'r')
legend({'2x','4x'})
hold off

[shravan]

Thank you Frieidrich.it worked. Not clear with function handles.. any reference with more examples ?

[Friedrich]

Mhh, maybe have a look at the documentation:

http://www.mathworks.com/help/techdoc/matlab_prog/f2-38133.html

Or

http://www.mathworks.com/help/techdoc/ref/function_handle.html