Created attachment 766 [details] matrixQ extraction with SparseQR (working) and SPQR The method I've used with SparseQR to extract the Q matrix - multiplying on the right by a dense identity matrix - does not work with SPQR, producing instead a compile error within Cholmod that looks like a trait extraction issue of some sort: Eigen/src/CholmodSupport/CholmodSupport.h:143:47: error: third operand to the conditional operator is of type ‘void’, but the second operand is neither a throw-expression nor of type ‘void’ res.d = Derived::IsVectorAtCompileTime ? mat.derived().size() : mat.derived() ^ Eigen/src/CholmodSupport/CholmodSupport.h:144:14: error: ‘class Eigen::CwiseNullaryOp<Eigen::internal::scalar_identity_op<double>, Eigen::Matrix<double, -1, -1> >’ has no member named ‘data’ res.x = (void*)(mat.derived().data()); A reduced test case is attached.
You can workaround with: MatrixXd I = MatrixXd::Identity(mat.rows(), mat.cols()); MatrixXd Q_ss = QR_ss.matrixQ() * I;
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