docs: public static double elementMinAbs( DMatrix2x2 a ) {
          double min = Math.abs(a.a11);
          double tmp = Math.abs(a.a12); if( tmp < min ) min = tmp;
          tmp = Math.abs(a.a21); if( tmp < min ) min = tmp;
          tmp = Math.abs(a.a22); if( tmp < min ) min = tmp;
  
          return min;
      }