docs: public static double elementMaxAbs( DMatrix4 a ) {
          double max = Math.abs(a.a1);
          double tmp = Math.abs(a.a2); if( tmp > max ) max = tmp;
          tmp = Math.abs(a.a2); if( tmp > max ) max = tmp;
          tmp = Math.abs(a.a3); if( tmp > max ) max = tmp;
          tmp = Math.abs(a.a4); if( tmp > max ) max = tmp;
  
          return max;
      }