docs: public static DMatrix4 extractRow( DMatrix4x4 a , int row , DMatrix4 out ) {
          if( out == null) out = new DMatrix4();
          switch( row ) {
              case 0:
                  out.a1 = a.a11;
                  out.a2 = a.a12;
                  out.a3 = a.a13;
                  out.a4 = a.a14;
              break;
              case 1:
                  out.a1 = a.a21;
                  out.a2 = a.a22;
                  out.a3 = a.a23;
                  out.a4 = a.a24;
              break;
              case 2:
                  out.a1 = a.a31;
                  out.a2 = a.a32;
                  out.a3 = a.a33;
                  out.a4 = a.a34;
              break;
              case 3:
                  out.a1 = a.a41;
                  out.a2 = a.a42;
                  out.a3 = a.a43;
                  out.a4 = a.a44;
              break;
              default:
                  throw new IllegalArgumentException("Out of bounds row.  row = "+row);
          }
          return out;
      }