Solving The Ordinary Least Squares in Closed Form, Without Inversion or Normalization

Abstract: By connecting the LU factorization and the Gram-Schmidt orthogonalization without any normalization, closed-forms for the coefficients of the ordinary least squares estimates are presented. Instead of using matrix inversion explicitly, each of the coefficients is expressed and computed directly as a linear combination of non-normalized Gram-Schmidt vectors and the original data matrix and also in terms of the upper triangular factor from LU factorization. The coefficients may computed iteratively using backward or forward algorithms given.