ordinary least squares
[bhat,ixpx]=ols0(y,x)
* y = dependent variable vector (nobs x 1)
* x = independent variables matrix (nobs x nvar)
* bhat = estimated beta in y = x*beta+u
* ixpx = inverse of matrix x'*x
x=grand(15,3,'nor',0,1) y=x*ones(3,1)+grand(15,1,'nor',0,1) b=ols0(y,x)