second order differential equation

Hi, I wanted to know where I was wrong in the program because the plot should come with a spiral and not a straight line

 u=0.1; %damping parameter
 h=0.4; %sampling step

x(1) = 2; %initial values
y(1) = 1.5;   

 for k=1:200
      %runge kutta 4th order 
      K1=h*vandp(x(k), y(k));
      K2=h*vandp(x(k)+h/2, y(k)+K1/2);
      K3=h*vandp(x(k)+h/2, y(k)+K2/2);
      K4=h*vandp(x(k)+h, y(k)+K3);
      y(k+1) = y(k) + K1/6+K2/3+K3/3+K4/6;
      x(k+1) = h + x(k);    
 end

plot(x,y);

%%%%%%%%%%%%%%%%%%%

%function van der pol 
function van = vandp(x,y)

u = 0.1; 
x(1) = 2; 
y(1) = 1.5;

van=-u*(x^2-1)*y-x;

Answer 1

[Torsten]

function van = vandp(x,y)

u = 0.1; 
%x(1) = 2; 
%y(1) = 1.5;

van=-u*(x^2-1)*y-x;

Best wishes

Torsten.

[Kevin Savic]

There are two separate programs, if you comment the initial values, matlab will give me a mistake saying that i did not put x and y

[Torsten]

Try to put it in one file, name it "main.m":

function main
u = 0.1; %damping parameter
h = 0.4; %sampling step
x(1) = 2; %initial values
y(1) = 1.5;   

 for k=1:200
      %runge kutta 4th order 
      K1=h*vandp(x(k), y(k));
      K2=h*vandp(x(k)+h/2, y(k)+K1/2);
      K3=h*vandp(x(k)+h/2, y(k)+K2/2);
      K4=h*vandp(x(k)+h, y(k)+K3);
      y(k+1) = y(k) + K1/6+K2/3+K3/3+K4/6;
      x(k+1) = h + x(k);    
 end
plot(x,y);

%%%%%%%%%%%%%%%%%%%

function van = vandp(x,y)

u = 0.1; 
van = -u*(x^2-1)*y-x;

[Kevin Savic]

Ok now is working, thank you very much