code: public VectorIterator iteratorOfRow(int i) {
          final int ii = i;
          return new VectorIterator(columns) {
              private int j = -1;
  
              @Override
              public int index() {
                  return j;
              }
  
              @Override
              public double get() {
                  return Matrix.this.get(ii, j);
              }
  
              @Override
              public void set(double value) {
                  Matrix.this.set(ii, j, value);
              }
  
              @Override
              public boolean hasNext() {
                  return j + 1 < columns;
              }
  
              @Override
              public Double next() {
                  if(!hasNext()) {
                      throw new NoSuchElementException();
                  }
                  j++;
                  return get();
              }
          };
      }
docs: Returns a vector iterator of the given row {code i}.
  
  @return a vector iterator