use matlab to represent equations

i am now trying to use use matlab to represent equations

come up with:

 t1=0;
t2=0;
for n=1:N-2
r1=(1/(N-1))*x(n)*x(n+1); 
r2=(1/(N-2))*x(n)*x(n+2); 
t1=t1+r2+((r2)^2+8*(r1)^2)^(1/2);
end
for n=1:N-1
r1=(1/(N-1))*x(n)*x(n+1);  
t2=t2+4*r1;
end

 r = t1/t2;
if (r>1)
r=1;
end
if (r<-1)
r=-1;
end
w=acos(r);

it does not seem to work, could anyone help to correct? thank you!

[modified covariance]

N=max(size(x));

[Jan]

"It does not seem to work" is not a helpful description of the occurring problems. Please be so kind and explain the difference between the results and your expectations.

Answer 1

[Pedro Villena]

fs = 1000;  % samplig frequency [Hz]
t = 0:1/fs:0.1-1/fs; % time vector
w = 267*pi; % oscilation frequency [rad/s] (133.5 Hz)
p = 1.2;    % phase [rad] (68.7549 deg)
x = 10*cos(w*t+p); % wave vector

N=length(x);   % N:number of values
r=zeros(1,3);  % r={r0,r1,r2}
for k=0:2,     % k=0,1,2
    n=(0:N-1-k);
    r(k+1) = sum(x(n+1).*x(n+1+k))/(N-k);
end
w0 = fs*acos((r(3)+sqrt(r(3)^2+8*r(2)^2))/(4*r(2))); % [rad/s]
fprintf('w0 = %f rad/s = %f Hz\n',w0,w0/2/pi);

[modified covariance]

i have to express my sincere gratitude to you. it works!!