Multiplying eigen sparse matrix with a C array

Question

I have an eigen sparse matrix and I would like to multiply it with a vector. However, my vector is stored in a STL vector container because of the way the whole thing is designed. So, I have something like:

std::vector<float> values;
Eigen::SparseMatrix<float> some_mat;

// fill the matrix and vector
....
float * vec = &values[0];

Now is there a way to do something like:

some_mat * vec;

Without copying the vector into an eigen vector object. If there is no way around the copy, what would be the most efficient way to copy an STL vector or a C-array to an eigen VectorXf object?

Answer 1

You can use Eigen::Map for that purpose:

VectorXd res = some_mat * VectorXf::Map(vec, size);

Note that Map object are read-write, so res could also be a Map .