Let's say your function is f(x,y)=2x+y. You need to create this function prior you send it to your backEuler:
f=@(x,y)2*x+y;
backEuler(f,2,3,0,0);
The above lines go into the Command Window. Now, your backEuler function could be a separate file .m-function:
function backEuler(f,x0,y0,h,N)
x(1)=x0;
y(1)=y0;
for i=1:N
x(i+1)=x(i)+h;
y_temp=y(i)+h*x(i)*x(i);
y(i+1)=y(i)+h*f(x(i+1),y_new);
end
plot(x,y);
end
Just file->new->function, paste the above script and save it as backEuler (make sure that matlab does not have the function with the same name). Also, to use this function you need to set matlab to a current folder. That's it.
