Runga Kutta Mthod 4

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Ali
Ali on 13 Nov 2020
Edited: Alan Stevens on 14 Nov 2020
I want to solve second order equation through Ruga kutta method .Please check what is error in this code
%input paramters
m=100;
k=25000;
e=100;
F=15000;
w=(k/m)^0.5;
t(1)=0;
x(1)=0;
v(1)=1;
h=0.1;
tfinal=100;
N=ceil((tfinal-t(1))/h);
f1=@(t,x,v) v;
f2=@(t,x,v) -(k/m)*v-(e/m)*x+(F/m)*cos(w*t);
for j=1:N;
t(j+1)=t(j)+h;
K1x=f1(t(j),x(j),v(j));
K1v=f2(t(j),x(j),v(j));
K2x=f1(t(j)+h/2,x(j)+h/2*K1x,v(j)+h/2*K1v);
K2v=f2(t(j)+h/2,x(j)+h/2*K1x,v(j)+h/2*K1v);
K3x=f1(t(j)+h/2,x(j)+h/2*K2x,v(j)+h/2*K2v);
K3v=f2(t(j)+h/2,x(j)+h/2*K2x,v(j)+h/2*K2v);
K4x=f1(t(j)+h,x(j)+h*K3x,v(j)+h*K3v);
K4v=f2(t(j)+h,x(j)+h*K3x,v(j)+h*K3v);
x(j+1)=x(j)+h/6*(K1x+2*K2x+2*K3x+K4x);
v(j+1)=v(j)+h/6*(K1v+2*K2v+2*K3v+K4v);
end
disp(x(N));
figure;
plot(t,x,'lineWidth',1);

Accepted Answer

Alan Stevens
Alan Stevens on 14 Nov 2020
Edited: Alan Stevens on 14 Nov 2020
As before, your value for h is too large. Set h = 0.01 and it works!

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