docs: public static DMatrix2 extractRow( DMatrix2x2 a , int row , DMatrix2 out ) {
          if( out == null) out = new DMatrix2();
          switch( row ) {
              case 0:
                  out.a1 = a.a11;
                  out.a2 = a.a12;
              break;
              case 1:
                  out.a1 = a.a21;
                  out.a2 = a.a22;
              break;
              default:
                  throw new IllegalArgumentException("Out of bounds row.  row = "+row);
          }
          return out;
      }