message: operator documentation
diff: // http://opensource.org/licenses/MIT>, at your option. This file may not be
  // copied, modified, or distributed except according to those terms.
  -//! TODO DOCUMENTATION
  +//! # `ArgminOperator`
  //!
  +//! `ArgminOperator` stores relevant information for systems of linear equations which are written
  +//! as `y = Ax`.
  use std;
  use ndarray::{Array1, Array2};
  