How to convert sparse matrix to dense matrix in Eigen

20
votes

Is there some easy and fast way to convert a sparse matrix to a dense matrix of doubles?

Because my SparseMatrix is not sparse any more, but became dense after some matrix products.

Another question I have: The Eigen library has excellent performance, how is this possible? I don't understand why, because there are only header files, no compiled source.

1
c++matrixsparse-matrixeigen
What does performance have to do with whether code is in .h files or in .cpp files? – us2012
To understand how Eigen works and what makes it fast, have a better look at their docs (e.g. What happens inside) (which seeing the number of your questions would be useful in any case), and pick up a book on advance C++ and template programming. In any case, you should remove that question here and make a new one for it if after this you still are not sure about some details of how it works. – sgvd

1 Answers

43
votes

Let's declare two matrices:

SparseMatrix<double> spMat;
MatrixXd dMat;

Sparse to dense:

dMat = MatrixXd(spMat);

Dense to sparse:

spMat = dMat.sparseView();