code: public Matrix<E> set(E element, int x, int y) {
  		if (this.columns.size() < x) {
  			columns.set(x, new ArrayList<>());
  		}
  		this.columns.get(x).set(y, element);
  		return this;
  	}
docs: Sets the element {@code element} to the {@code (x, y)} position of the matrix
  
  @param element The element to be set
  @param x       The row
  @param y       The column
  @return {@code this}