在类中初始化模板对象（C ++）

Question

I want to denfine a class based on the Eigen library:

header file:

#include <Eigen>

using namespace Eigen;

class MatrixV{
    public:
        MatrixV(double mu, double omega, double delta, double size);
        Eigen::MatrixXd getV();
    private:
        Eigen::MatrixXd V;
        Eigen::JacobiSVD<Eigen::MatrixXd, Eigen::NoQRPreconditioner> svd(V, ComputeFullU | ComputeFullV);
};

cpp-file:

MatrixV::MatrixV(double mu, double omega, double delta, double size){
    Eigen::MatrixXd V = MatrixXd::Random(3,3)
}

Eigen::MatrixXd MatrixV::getV(){
    return V;
}

By compiling that code, my compiler gives me the following errors:

MatrixV.h:14:68: error: 'V' is not a type
   Eigen::JacobiSVD<Eigen::MatrixXd, Eigen::NoQRPreconditioner> svd(V,ComputeFullU | ComputeFullV);

MatrixV.h:14:71: error: 'ComputeFullU' is not a type
   Eigen::JacobiSVD<Eigen::MatrixXd, Eigen::NoQRPreconditioner> svd(V, ComputeFullU | ComputeFullV);

MatrixV.h:14:84: error: expected ',' or '...' before '|' token
   Eigen::JacobiSVD<Eigen::MatrixXd, Eigen::NoQRPreconditioner> svd(V, ComputeFullU | ComputeFullV);
                                                                              So the main problem seems to be the line 
Eigen::JacobiSVD<Eigen::MatrixXd, Eigen::NoQRPreconditioner> svd(V, ComputeFullU | ComputeFullV);

but I just copy-pasted it from http://eigen.tuxfamily.org/dox/classEigen_1_1JacobiSVD.html and I also don't understand why he expects type names in the ()-brackets anyway. Do you have any Ideas? Thanks a lot!

Answer 1

Your error messages:

MatrixV.h:14:68: error: 'V' is not a type
   Eigen::JacobiSVD<Eigen::MatrixXd, Eigen::NoQRPreconditioner> svd(V,ComputeFullU | ComputeFullV);

MatrixV.h:14:71: error: 'ComputeFullU' is not a type
   Eigen::JacobiSVD<Eigen::MatrixXd, Eigen::NoQRPreconditioner> svd(V, ComputeFullU | ComputeFullV);

MatrixV.h:14:84: error: expected ',' or '...' before '|' token
   Eigen::JacobiSVD<Eigen::MatrixXd, Eigen::NoQRPreconditioner> svd(V, ComputeFullU | ComputeFullV);

are all caused by the same issue. The compiler thinks you're declaring a function, but it looks like you want to declare a variable svd . What you should do is to remove the parenthesis, and move it to the constructor:

#include <Eigen>

using namespace Eigen;

class MatrixV{
    public:
        MatrixV(double mu, double omega, double delta, double size);
        Eigen::MatrixXd getV();
    private:
        Eigen::MatrixXd V;
        Eigen::JacobiSVD<Eigen::MatrixXd, Eigen::NoQRPreconditioner> svd;
};

And change the constructor:

MatrixV::MatrixV(double mu, double omega, double delta, double size) {
    V = MatrixXd::Random(3,3)
    svd.compute(V, ComputeFullU | ComputeFullV);
}