Error:指向绑定函数的指针只能用于调用函数

 a1.determinant;

改为： a1.determinant();

    Eigen::MatrixXd a1(2,2);//ImagePoint
    a1<<n1,p1,n2,p2;
    double A1=a1.determinant;

改为：

    Eigen::MatrixXd a1(2,2);//ImagePoint
    a1<<n1,p1,n2,p2;
    double A1=a1.determinant();