I tried writing an Ordinary Differential Equation in MATLAB.
I wrote this code:
function [y] = odefun(t,y)
t = [0:0.01:10];
y = [0 0]';
y(1) = y(2);
y(2) = sin(2*t)-2*y(2)-2*y(1); % I get an error here
end
I get an error in the last line in this code. MATLAB doesn't show me what the error is. It just tells me I have an error in that line.
Why do I get this error and how to resolve it?
You try to assign to y(2) a vector of 1001 elements:
>> size(sin(2*t)-2*y(2)-2*y(1))
ans =
1 1001
The error message is pretty clear:
In an assignment A(:) = B, the number of elements in A and B must be the same.
Also, y and t are never use since you redefined them in the function.
What you want is to carefully read the documentation of the diverse ode solvers and the examples there and then correct your code to something like
% Solve ODE y''(t)+2*y'(t)+2*y(t) = sin(2*t), y(0)=y'(0)=0
function ydot = odefun(t,y)
ydot = zeros_like(y)
ydot(1) = y(2);
ydot(2) = sin(2*t)-2*y(2)-2*y(1);
end
% or
% odefun = @(y,t) [ y(2); sin(2*t)-2*y(2)-2*y(1) ]
% define sample points
tspan = [0:0.01:10];
% define initial value to t=tspan(1)
y0 = [0 0]';
[ t, y ] = ode45(odefunc, tspan, y0)
% t,y now contain the times and values that
% the solution was actually computed for.
