docs: public static double elementMin( DMatrix3x3 a ) {
          double min = a.a11;
          if( a.a12 < min ) min = a.a12;
          if( a.a13 < min ) min = a.a13;
          if( a.a21 < min ) min = a.a21;
          if( a.a22 < min ) min = a.a22;
          if( a.a23 < min ) min = a.a23;
          if( a.a31 < min ) min = a.a31;
          if( a.a32 < min ) min = a.a32;
          if( a.a33 < min ) min = a.a33;
  
          return min;
      }