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Asked by freestyler000218
on 28 Mar 2012

Ok, I have a second order ODE and I need to solve it using Runge-Kutta 4. I know that I have to make it into 2 first order equations.

So what I have is x''+1.14x'+3.14x=2.14cos(t)

I make this look like...

x'=v

x''=dvdt=2.14cos(t)-1.14v-3.14x

my step size is h=1.

and i am going from t=0 to t=5

initial conditions are x(0)=1 and x'(0)=0

I can solve this by hand on paper, however I am not too clear on how to write this out in MATLAB. Any help with the coding is greatly appreciated.

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Answer by Honglei Chen
on 28 Mar 2012

You can use `ode45`. You first define a function for your differential equation

function dy = myode(t,y) dy = zeros(2,1); dy(1) = y(2); dy(2) = 2.14*cos(t)-1.14*y(2)-3.14*y(1);

then you can call `ode45` with your initial conditions

[T,Y] = ode45(@myode,0:5,[1;0])

Answer by freestyler000218
on 28 Mar 2012

is there a way to do this **without** using ode45? I saw examples of code where people were using something like "feval"

Matt Tearle
on 28 Mar 2012

Why would you want to? ode45 is an adaptive stepsize 4th-order method, so it's going to do a better job than the vanilla RK4 we all know and love from our differential equations course.

And you don't need feval, even if you do want to write your own. You can just call a function, either hard-coded or passed to a function as a function handle.

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