docs: public Vec getColumnView(final int j)
      {
          final Matrix M = this;
          return new Vec() 
          {
              private static final long serialVersionUID = 7107290189250645384L;
  
              @Override
              public int length()
              {
                  return rows();
              }
  
              @Override
              public double get(int index)
              {
                  return M.get(index, j);
              }
  
              @Override
              public void set(int index, double val)
              {
                  M.set(index, j, val);
              }
  
              @Override
              public boolean isSparse()
              {
                  return M.isSparce();
              }
  
              @Override
              public Vec clone()
              {
                  if(M.isSparce())
                      return new SparseVector(this);
                  else
                      return new DenseVector(this);
              }
  
              @Override
              public void setLength(int length)
              {
                  throw new UnsupportedOperationException("Vector view can't not extend original matrix"); 
              }
          };
      }