I am doing runge kutta order 4 for a system of equations.Any bugs that giving me x1 and x2 =0 for all 200 values?

 function[]= xp(n,t,x,i) 
k(1,i+1)=-3*x(2);
k(2,i+1)=(1/3)*x(1); (differential equations)
end
 function[]= abc(n,h,t,step)
global x;
x=zeros(3);
disp(0)
disp(t)
disp(x(1))
k=zeros(step-1,4 ) ;
y=zeros(step-1,4 ) ;
for j=1:step
    xp(n,t,x,1)
    for i=1:n
        y(i)=x(i)+(1/2)*h*k(i,1);
    end
    xp(n,t+h/2,y,2)
    for i=1:n
        y(i)=x(i)+(1/2)*h*k(i,2);
    end
    xp(n,t+(h/2),y,3)
    for i=1:n
        y(i)= x(i)+(1/2)*h*k(i,3);
    end
    xp(n,t+h,y,k(i,4))
    for i=1:n
        x(i)=k(i)+(1/6)*h*(k(i,1)+k(i,2)+k(i,3)+k(i,4));
    end
    t=t+h;
    disp(j)
    disp(t)
    disp(x(1))
    disp(x(2))
  end
end
 function []=test1()
n=2;
step=100;
a=0;
b=4;
t=0;
x(1)=0; % initial condition
x(2)=1; % initial condition
h=(b-a)/step;
abc(n,h,t,step)
end

Answer 1

[Abraham Boayue]

See this link, it might be helpful. https://www.mathworks.com/matlabcentral/answers/386695-how-to-solve-this#answer_308949