let ols_regression ?(i=true) x y =
let b = 1 in
let s = optimal_rate in
let t = when_stable in
let l = square_loss in
let g = square_grad in
let r = noreg in
let o = noreg_grad in
let a = 0. in
let p = MX.(uniform (col_num x) (col_num y)) in
_sgd_basic b s t l g r o a i p x y