cannot convert ‘std::vector

I can't convert the double to double here in main.h I have :

std::vector<std::vector<double>> *m_va;

std::vector<std::vector<double> > *get_ptr() { return m_va; }

in main.cpp I want to have :

std::vector<double *> F(n);

F[i] = this->get_ptr()[j].data();

but I got : cannot convert ‘std::vector’ to ‘__gnu_cxx::__alloc_traitsstd::allocator<double*, double>::value_type’ {aka ‘double*’}