Matlab coding explicit midpoint method coding,

%Where i have a separate file lorenz.m which contains

%function [ dx ] = lorenz( t,x ) %sig=10; %beta=8/3 %rho=28; %dx=[-sig*x(1)+sig*x(2); rho*x(1)-x(2)-x(1)*x(3);-beta*x(3)+x(1)*x(2)]; %end

function [ t,x ] = RK2(lorenz,t0,tn,n ) t(1)=t0 x(:,1)=[1 1 1] h=(tn-t0)/n

for k=1:n

d1=lorenz(t(k),x(:,k))
d2=lorenz((t(k)+h/2), x(:,k)+(d1)/2);
x(:,k+1)=x(:,k)+h*d2

end

If I try to solve this in script [t x]=RK2(lorenz,0,100,100000) for t=0 to 100 and h=0.0001 so that n steps are 100000, I keep getting error.... can you guys help???