How do I make a diagonal matrix in eigen with a dynamic size?

Question

I want to make a diagonal matrix with the C++ linear algebra library eigen, but I do not know the size of the matrix during compile time. Hence,

DiagonalMatrix<Scalar, SizeAtCompileTime> diag1(size);

will not work. The values along the diagonal also differ. Help?

Answer 1

You need to instantiate the template parameter with what is relevant for you:

DiagonalMatrix<double,Eigen::Dynamic> diag1(size);