In the following code, I declare and initialize a 5x5 sparse matrix and set the (0,0) value to 1; matrix A is row major, matrix B is column major. I run over the outer index and through the inner iterator in each case identically. However, when I run the code - with matrix B, I get a "1" printed out - as expected; with matrix A I get an absurd number. I encountered this while trying to implement a mean calculation for a sparse matrix. Here's a bit of sample code to demonstrate the problem as discussed above. Yes, I know some of the header stuff is unnecessary; I just nabbed it from another demo I was working on: #include <iostream> #include <Eigen/Dense> #include <Eigen/Sparse> using namespace Eigen; using namespace std; int main() { SparseMatrix<float,RowMajor> A(5,5); A.insert(0,0)=1; for (int k = 0; k<A.outerSize(); ++k) for (SparseMatrix<float>::InnerIterator it(A,k); it; ++it) std::cout<<it.value()<<std::endl; SparseMatrix<float,ColMajor> B(5,5); B.insert(0,0)=1; for (int k = 0; k<B.outerSize(); ++k) for (SparseMatrix<float>::InnerIterator it(B,k); it; ++it) std::cout<<it.value()<<std::endl; }

(In reply to comment #0) > SparseMatrix<float,RowMajor> A(5,5); > > A.insert(0,0)=1; > > for (int k = 0; k<A.outerSize(); ++k) > for (SparseMatrix<float>::InnerIterator it(A,k); it; ++it) > std::cout<<it.value()<<std::endl; You must use SparseMatrix<float, ColMajor>::InnerIterator. I guess what happens is that A is converted to a temporary ColMajor matrix which gets invalid before it.value() is called. We should catch that somehow, maybe by adding a constructor for invalid types which results in a static assertion. I assume things like the following won't work properly, either: typedef SparseMatrix<float> Sparse; Sparse A, B; // initialize somehow Sparse::InnerIterator(A+B, 0); // Iterator to a temporary

This has been fixed a few weeks ago for SparseMatrix: https://bitbucket.org/eigen/eigen/commits/afd3e37726ef and for SparseVector: https://bitbucket.org/eigen/eigen/commits/4a1386d13502/

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