x = [0 1 2]';
y = [3/2 0 3/2]';

X = [[1 1 1]' x];
C = [1 0.8 0; 0.8 1 0; 0 0 1];
% C = eye(3);
Cinv = C^(-1);

H =  (X' * Cinv * X)^(-1) * X' * Cinv ;
betahat = H*y;