/* new way of calculating b's. using only covariance matrix */
/* tested against current way, gives same answer to 3d decimal place.
   investigate numerical stability against current qr method  */
/* WHy same answer to W=I, not same answer after 2nd stage GMM? */

w11 = w[1,1];
w12 = w[1,2:cols(w)];
w21 = w[2:rows(w),1];
w22 = w[2:rows(w), 2:cols(w)];

f = _factors[.,2:cols(_factors)];
r = _allr[.,2:cols(_allr)];
rbar = meanc(r);
covs = 1/T*(f-meanc(f)')'(r - rbar');
invtrm = inv(covs*w22*covs');
b0str = w11 + rbar'w21 - (w12 + rbar'w22)*covs'*invtrm*covs*w21;
b0str = b0str/(w11 + w12*rbar + rbar'w21 + rbar'w22*rbar -
        (w12 + rbar'w22)*covs'*invtrm*covs*(w22*rbar + w21) );
b1 = invtrm*covs*(w21 - (w22*rbar + w21)*b0str);
b0 = b0str - meanc(f)'b1;

/* old b */

bcov = 1/T*(_factors)'(_allr);
bbig = inv(bcov*W*bcov')*bcov*W*_price;

b0~b1'; b';bbig';