Applying the method of lines to a partial differential equation and using Runge-kutta method

Question

By method of lines I converted the PDE (heat equation)

$$u_t=u_{xx},$$ with the initial and boundary conditions \begin{align} u(0,t)&=u(0.1,t) \\ u(0,x)&=\sin(2 \pi x) \end{align} to a system of ODEs, as follows

function ut=pde1(t,u)
%
% Problem parameters
 % global ncall
  xl=0.0;
  xr=1.0;
  d=10;
  a=10;
%
% PDE
  n=length(u);
  h=((xr-xl)/(n-1));
  for i=1:n
    if(i==1)     ut(i)=0.0;
    elseif(i==n) ut(i)=0;
    else         ut(i)=d*(u(i+1)-2.0*u(i)+u(i-1))/h^2;
    end
  end
  ut=ut';
%

Now I am solving the ODEs ut by Runge-kutta method as follows:

%Initial condition
  n=500;
  for i=1:n
    u0(i)=sin((2*pi)*(i-1)/(n-1));
  end
  t0=0.0;
  tf=0.1;
  tout=linspace(t0,tf,n);
    y=zeros(n,length(tout));
 y(:,1)=u0';
    h=1/n;
    
    for i = 1 : length(tout)
        t=tout(i);
         k1 = pde_1(t,y(:,i));
         k2 = pde_1(t+h/2, y(:,i)+h*k1/2);
         k3 = pde_1(t+h/2, y(:,i)+h*k2/2);
         k4 = pde_1(t+h, y(:,i)+h*k3);
         y(:,i+1) = y(:,i) + h*(k1 + 2*k2 + 2*k3 + k4)/6;
        
    end
 
    y  
    plot(tout,y(:,1))

but the outputs are NAN! any help?