Why is my code not working??

   function [T , Y] = pendulum_RK4(f,tspan,y0,n)
   % Solves y' = f(t,y) with initial condition y(a) = y0
   % on the interval [a,b] using n steps of the 4th order runge kutta method.
   % y and f may be column vectors
   % Dimension y0 must equal that of y and f
   % T shall be a n+1 column vector
   % Y shall be a (n+1) by d matrix (d is the length of y)
   a = tspan(1);
   b = tspan(2);
    % Step size:
   h = (b-a)/n;
   % t and y are current variables:
    t = a; y = y0; 
   % T and Y will record all steps:
   T = a; Y = y0';
   for i = 1:n
   k1 = h*f(t,y);
   k2 = h*f(t+(0.5*h),y+(0.5*k1));
   k3 = h*f(t+(0.5*h),y+(0.5*k2));
   k4 = h*f(t+h,y+k3);
   y = y + (1/6)*k1 + (1/3)*k2 + (1/3)*k3 + (1/6)*k4;
   t = a + i*h;
   T = [T; t];
   Y = [Y; y'];
   end

    >>  f =    inline('[y(2);-9.81*sin(y(1))-(6.25*0.25)*cos(y(1))*sin(2.5*t)]','t','y')
    >> [T Y] = pendulum_RK4(f,[0 10],[0;0],1000)
    >> theta = Y(:,1);
    >>plot(T,theta)

[Zhang lu]

it can work well in my computer

whats your error message?

do your M file in your matlab current folder ?