Try to solve A*x = B where A is sparse symmetric.

#include <Eigen/Sparse>
#include <Eigen/SparseExtra>
...

SimplicialLDLt<SparseMatrix<float> > solver;
solver.compute(Lu);


Error: SimplicialLDLt: undeclared undentifier

Anything missing?

Thanks

SimplicialCholesky<SparseMatrix<float> > solver;

solves the problem

SimplicialLDLt is only available in the default branch. You where probably using Eigen 3.0.x.