How to convert sparse matrix to dense matrix in Eigen

Question

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.

What does performance have to do with whether code is in `.h` files or in `.cpp` files? — us2012, Mar 21 '13 at 21:14
To understand how Eigen works and what makes it fast, have a better look at their docs (e.g. [What happens inside](http://eigen.tuxfamily.org/dox/TopicInsideEigenExample.html)) (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, Mar 23 '13 at 14:50

score 47 · Accepted Answer · edited Aug 10 '15 at 23:38

47

Let's declare two matrices:

SparseMatrix<double> spMat;
MatrixXd dMat;

Sparse to dense:

dMat = MatrixXd(spMat);

Dense to sparse:

spMat = dMat.sparseView();

edited Aug 10 '15 at 23:38

Michael Koval

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answered Mar 23 '13 at 21:29

ggael

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How to convert sparse matrix to dense matrix in Eigen

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