docs: public static void multTransAB( double alpha , DMatrix2x2 a , DMatrix2x2 b , DMatrix2x2 c) {
          c.a11 = alpha*(a.a11*b.a11 + a.a21*b.a12);
          c.a12 = alpha*(a.a11*b.a21 + a.a21*b.a22);
          c.a21 = alpha*(a.a12*b.a11 + a.a22*b.a12);
          c.a22 = alpha*(a.a12*b.a21 + a.a22*b.a22);
      }