using https://github.com/mtao/core for a grid datastructure, this code creates a somewhat-virtual matrix that produces a horizontal stack of grid vertices and use-driven data (extra vertices). based off of https://eigen.tuxfamily.org/dox/TopicCustomizing_NullaryExpr.html

grid_vertex_stacker.cpp

#include <Eigen/Dense>
#include <iostream>
#include <mtao/geometry/grid/grid.h>
template<class ArgType, int D>
struct col_offset_helper {
    typedef Eigen::Matrix<typename ArgType::Scalar,
            D,
            Eigen::Dynamic,
            Eigen::ColMajor,
            D,
            Eigen::Dynamic
                > MatrixType;
};
template <typename MatrixType>
class col_offset {
    const MatrixType V;
    mtao::geometry::grid::GridD<typename MatrixType::Scalar,MatrixType::RowsAtCompileTime> grid;
    int offset_cols = 0;
    public:
    template <typename Derived, typename... Args>
        col_offset(const Eigen::MatrixBase<Derived>& v, Args&&... args): V(v), grid(std::forward<Args>(args)...) {}
    const typename MatrixType::Scalar operator()(int row, int col) const {
        if(col >= grid.size()) {
            return V(row, col-grid.size());
        } else {
            return grid.vertex(col)(row);
        }
    }
};

template <int D, typename ArgType, typename... Args>
Eigen::CwiseNullaryOp<col_offset<ArgType>, typename col_offset_helper<ArgType,D>::MatrixType>
make_col_offset(const Eigen::MatrixBase<ArgType>& arg, Args&&... args) {
    using MatType = typename col_offset_helper<ArgType,D>::MatrixType;
    mtao::geometry::grid::GridD<typename ArgType::Scalar,D> grid(std::forward<Args>(args)...);
    return MatType::NullaryExpr(arg.cols(), arg.cols()+grid.size(), col_offset<ArgType>(arg.derived(), grid));
}

int main() {
    auto I = Eigen::Matrix3d::Random().eval();
    auto F = make_col_offset<3>(I,std::array<int,3>{{3,3,3}});
    std::cout << F << std::endl;
    std::cout << "Rows: " << std::endl;
    for(int i = 0; i < F.rows(); ++i) {
        std::cout << i << "): " << F.row(i) << std::endl;
    }
}

Output generated:

        0       0.5         1         0       0.5         1         0       0.5         1         0       0.5         1         0       0.5         1         0       0.5         1         0       0.5         1         0       0.5         1         0       0.5         1  0.680375   0.59688 -0.329554
        0         0         0       0.5       0.5       0.5         1         1         1         0         0         0       0.5       0.5       0.5         1         1         1         0         0         0       0.5       0.5       0.5         1         1         1 -0.211234  0.823295  0.536459
        0         0         0         0         0         0         0         0         0       0.5       0.5       0.5       0.5       0.5       0.5       0.5       0.5       0.5         1         1         1         1         1         1         1         1         1  0.566198 -0.604897 -0.444451
Rows: 
0):         0       0.5         1         0       0.5         1         0       0.5         1         0       0.5         1         0       0.5         1         0       0.5         1         0       0.5         1         0       0.5         1         0       0.5         1  0.680375   0.59688 -0.329554
1):         0         0         0       0.5       0.5       0.5         1         1         1         0         0         0       0.5       0.5       0.5         1         1         1         0         0         0       0.5       0.5       0.5         1         1         1 -0.211234  0.823295  0.536459
2):         0         0         0         0         0         0         0         0         0       0.5       0.5       0.5       0.5       0.5       0.5       0.5       0.5       0.5         1         1         1         1         1         1         1         1         1  0.566198 -0.604897 -0.444451