Hello,

in the current development version of Eigen the documentation says that Eigen::SparseMatrixBase
contrains implementations of blocks which are non-const. Why does the following code fail to compile:

Code: Select all

#include <Eigen/Dense>
#include <Eigen/Sparse>

int main(){
        Eigen::SparseMatrix<double> m(2,2);
        m.block(0,0,1,1) = m.block(1,1,1,1);
}


with the error messages:

Code: Select all

g++ -Wall -I/home/wern_al/local/foreign_packages/eigen/build/install/include/eigen3/ test.cpp
/home/wern_al/local/foreign_packages/eigen/build/install/include/eigen3/Eigen/src/Core/util/XprHelper.h: In member function ‘Eigen::BlockImpl<Eigen::SparseMatrix<double, 0, int>, -0x000000001, -0x000000001, false, Eigen::Sparse>& Eigen::BlockImpl<Eigen::SparseMatrix<double, 0, int>, -0x000000001, -0x000000001, false, Eigen::Sparse>::operator=(const Eigen::BlockImpl<Eigen::SparseMatrix<double, 0, int>, -0x000000001, -0x000000001, false, Eigen::Sparse>&)’:
/home/wern_al/local/foreign_packages/eigen/build/install/include/eigen3/Eigen/src/Core/Block.h:100:   instantiated from ‘Eigen::Block<XprType, BlockRows, BlockCols, InnerPanel>& Eigen::Block<XprType, BlockRows, BlockCols, InnerPanel>::operator=(const Eigen::Block<XprType, BlockRows, BlockCols, InnerPanel>&) [with XprType = Eigen::SparseMatrix<double, 0, int>, int BlockRows = -0x000000001, int BlockCols = -0x000000001, bool InnerPanel = false]’
test.cpp:6:   instantiated from here
/home/wern_al/local/foreign_packages/eigen/build/install/include/eigen3/Eigen/src/Core/util/XprHelper.h:35: error: ‘Eigen::internal::no_assignment_operator& Eigen::internal::no_assignment_operator::operator=(const Eigen::internal::no_assignment_operator&)’ is private
/home/wern_al/local/foreign_packages/eigen/build/install/include/eigen3/Eigen/src/Core/Block.h:100: error: within this context
/home/wern_al/local/foreign_packages/eigen/build/install/include/eigen3/Eigen/src/Core/Block.h:100: error: non-static reference member ‘const Eigen::SparseMatrix<double, 0, int>& Eigen::BlockImpl<Eigen::SparseMatrix<double, 0, int>, -0x000000001, -0x000000001, false, Eigen::Sparse>::m_matrix’, can't use default assignment operator
/home/wern_al/local/foreign_packages/eigen/build/install/include/eigen3/Eigen/src/Core/Block.h:100: error: non-static const member ‘const Eigen::internal::variable_if_dynamic<int, -0x000000001> Eigen::BlockImpl<Eigen::SparseMatrix<double, 0, int>, -0x000000001, -0x000000001, false, Eigen::Sparse>::m_startRow’, can't use default assignment operator
/home/wern_al/local/foreign_packages/eigen/build/install/include/eigen3/Eigen/src/Core/Block.h:100: error: non-static const member ‘const Eigen::internal::variable_if_dynamic<int, -0x000000001> Eigen::BlockImpl<Eigen::SparseMatrix<double, 0, int>, -0x000000001, -0x000000001, false, Eigen::Sparse>::m_startCol’, can't use default assignment operator
/home/wern_al/local/foreign_packages/eigen/build/install/include/eigen3/Eigen/src/Core/Block.h:100: error: non-static const member ‘const Eigen::internal::variable_if_dynamic<int, -0x000000001> Eigen::BlockImpl<Eigen::SparseMatrix<double, 0, int>, -0x000000001, -0x000000001, false, Eigen::Sparse>::m_blockRows’, can't use default assignment operator
/home/wern_al/local/foreign_packages/eigen/build/install/include/eigen3/Eigen/src/Core/Block.h:100: error: non-static const member ‘const Eigen::internal::variable_if_dynamic<int, -0x000000001> Eigen::BlockImpl<Eigen::SparseMatrix<double, 0, int>, -0x000000001, -0x000000001, false, Eigen::Sparse>::m_blockCols’, can't use default assignment operator
/home/wern_al/local/foreign_packages/eigen/build/install/include/eigen3/Eigen/src/Core/Block.h: In member function ‘Eigen::Block<XprType, BlockRows, BlockCols, InnerPanel>& Eigen::Block<XprType, BlockRows, BlockCols, InnerPanel>::operator=(const Eigen::Block<XprType, BlockRows, BlockCols, InnerPanel>&) [with XprType = Eigen::SparseMatrix<double, 0, int>, int BlockRows = -0x000000001, int BlockCols = -0x000000001, bool InnerPanel = false]’:
/home/wern_al/local/foreign_packages/eigen/build/install/include/eigen3/Eigen/src/Core/Block.h:110: note: synthesized method ‘Eigen::BlockImpl<Eigen::SparseMatrix<double, 0, int>, -0x000000001, -0x000000001, false, Eigen::Sparse>& Eigen::BlockImpl<Eigen::SparseMatrix<double, 0, int>, -0x000000001, -0x000000001, false, Eigen::Sparse>::operator=(const Eigen::BlockImpl<Eigen::SparseMatrix<double, 0, int>, -0x000000001, -0x000000001, false, Eigen::Sparse>&)’ first required here


oh, then maybe the documentation has to be clarified. Only special blocks are writeable. This includes .col(), .leftCols(), .middleCols(), .rightCols() for a column major matrix and the row versions for a row major matrix. This limitation is to prevent writing completely inefficient code.

I see and understand. Just my two cents:

(1) Even though the performance critical part of my code uses SparseMatrix
in a read-only manner, an easy initialization of this matrix is not
straight forward.

(2) It would be very desirable to have a clearly defined common interface
to sparse and dense matrices. This is especially useful in templated code
which can otherwise be seamlessly switched from Dense to Sparse.


Alex

yes, I kind of agree with you and we are moving slowly towards this goal.