Eigen: vector of linear system solver - c++

Question

I'm working with the Eigen linear algebra library and need a vector of BiCGSTAB-solvers. Unfortunately, extending this vector is extremely difficult. The minimal (not) working example is
#include <Eigen/Eigen>
int main() {
std::vector< Eigen::BiCGSTAB< Eigen::SparseMatrix< double > > > tmp;
tmp.emplace_back();
}
and yields the error message
$ g++ -I/usr/include/eigen3 main.cpp
In file included from /usr/include/c++/12.2.0/vector:63,
from /usr/include/c++/12.2.0/functional:62,
from /usr/include/eigen3/Eigen/Core:85,
from /usr/include/eigen3/Eigen/Dense:1,
from /usr/include/eigen3/Eigen/Eigen:1,
from main.cpp:1:
/usr/include/c++/12.2.0/bits/stl_uninitialized.h: In instantiation of ‘constexpr bool std::__check_constructible() [with _ValueType = Eigen::BiCGSTAB<Eigen::SparseMatrix<double> >; _Tp = Eigen::BiCGSTAB<Eigen::SparseMatrix<double> >&&]’:
/usr/include/c++/12.2.0/bits/stl_uninitialized.h:182:4: required from ‘_ForwardIterator std::uninitialized_copy(_InputIterator, _InputIterator, _ForwardIterator) [with _InputIterator = move_iterator<Eigen::BiCGSTAB<Eigen::SparseMatrix<double> >*>; _ForwardIterator = Eigen::BiCGSTAB<Eigen::SparseMatrix<double> >*]’
/usr/include/c++/12.2.0/bits/stl_uninitialized.h:372:37: required from ‘_ForwardIterator std::__uninitialized_copy_a(_InputIterator, _InputIterator, _ForwardIterator, allocator<_Tp>&) [with _InputIterator = move_iterator<Eigen::BiCGSTAB<Eigen::SparseMatrix<double> >*>; _ForwardIterator = Eigen::BiCGSTAB<Eigen::SparseMatrix<double> >*; _Tp = Eigen::BiCGSTAB<Eigen::SparseMatrix<double> >]’
/usr/include/c++/12.2.0/bits/stl_uninitialized.h:397:2: required from ‘_ForwardIterator std::__uninitialized_move_if_noexcept_a(_InputIterator, _InputIterator, _ForwardIterator, _Allocator&) [with _InputIterator = Eigen::BiCGSTAB<Eigen::SparseMatrix<double> >*; _ForwardIterator = Eigen::BiCGSTAB<Eigen::SparseMatrix<double> >*; _Allocator = allocator<Eigen::BiCGSTAB<Eigen::SparseMatrix<double> > >]’
/usr/include/c++/12.2.0/bits/vector.tcc:487:3: required from ‘void std::vector<_Tp, _Alloc>::_M_realloc_insert(iterator, _Args&& ...) [with _Args = {}; _Tp = Eigen::BiCGSTAB<Eigen::SparseMatrix<double> >; _Alloc = std::allocator<Eigen::BiCGSTAB<Eigen::SparseMatrix<double> > >; iterator = std::vector<Eigen::BiCGSTAB<Eigen::SparseMatrix<double> > >::iterator]’
/usr/include/c++/12.2.0/bits/vector.tcc:123:21: required from ‘std::vector<_Tp, _Alloc>::reference std::vector<_Tp, _Alloc>::emplace_back(_Args&& ...) [with _Args = {}; _Tp = Eigen::BiCGSTAB<Eigen::SparseMatrix<double> >; _Alloc = std::allocator<Eigen::BiCGSTAB<Eigen::SparseMatrix<double> > >; reference = Eigen::BiCGSTAB<Eigen::SparseMatrix<double> >&]’
main.cpp:5:21: required from here
/usr/include/c++/12.2.0/bits/stl_uninitialized.h:90:56: error: static assertion failed: result type must be constructible from input type
90 | static_assert(is_constructible<_ValueType, _Tp>::value,
| ^~~~~
/usr/include/c++/12.2.0/bits/stl_uninitialized.h:90:56: note: ‘std::integral_constant<bool, false>::value’ evaluates to false
Trying to std::move is worse, i.e.
#include <Eigen/Eigen>
#include <utility>
int main() {
std::vector< Eigen::BiCGSTAB< Eigen::SparseMatrix< double > > > tmp;
Eigen::BiCGSTAB< Eigen::SparseMatrix< double > > solver;
tmp.push_back( std::move( solver ) );
}
leads to the error message
g++ -I/usr/include/eigen3 main.cpp
In file included from /usr/include/c++/12.2.0/x86_64-pc-linux-gnu/bits/c++allocator.h:33,
from /usr/include/c++/12.2.0/bits/allocator.h:46,
from /usr/include/c++/12.2.0/string:41,
from /usr/include/c++/12.2.0/bits/locale_classes.h:40,
from /usr/include/c++/12.2.0/bits/ios_base.h:41,
from /usr/include/c++/12.2.0/ios:42,
from /usr/include/c++/12.2.0/istream:38,
from /usr/include/c++/12.2.0/sstream:38,
from /usr/include/c++/12.2.0/complex:45,
from /usr/include/eigen3/Eigen/Core:50,
from /usr/include/eigen3/Eigen/Dense:1,
from /usr/include/eigen3/Eigen/Eigen:1,
from main.cpp:1:
/usr/include/c++/12.2.0/bits/new_allocator.h: In instantiation of ‘void std::__new_allocator<_Tp>::construct(_Up*, _Args&& ...) [with _Up = Eigen::BiCGSTAB<Eigen::SparseMatrix<double> >; _Args = {Eigen::BiCGSTAB<Eigen::SparseMatrix<double, 0, int>, Eigen::DiagonalPreconditioner<double> >}; _Tp = Eigen::BiCGSTAB<Eigen::SparseMatrix<double> >]’:
/usr/include/c++/12.2.0/bits/alloc_traits.h:516:17: required from ‘static void std::allocator_traits<std::allocator<_CharT> >::construct(allocator_type&, _Up*, _Args&& ...) [with _Up = Eigen::BiCGSTAB<Eigen::SparseMatrix<double> >; _Args = {Eigen::BiCGSTAB<Eigen::SparseMatrix<double, 0, int>, Eigen::DiagonalPreconditioner<double> >}; _Tp = Eigen::BiCGSTAB<Eigen::SparseMatrix<double> >; allocator_type = std::allocator<Eigen::BiCGSTAB<Eigen::SparseMatrix<double> > >]’
/usr/include/c++/12.2.0/bits/vector.tcc:117:30: required from ‘std::vector<_Tp, _Alloc>::reference std::vector<_Tp, _Alloc>::emplace_back(_Args&& ...) [with _Args = {Eigen::BiCGSTAB<Eigen::SparseMatrix<double, 0, int>, Eigen::DiagonalPreconditioner<double> >}; _Tp = Eigen::BiCGSTAB<Eigen::SparseMatrix<double> >; _Alloc = std::allocator<Eigen::BiCGSTAB<Eigen::SparseMatrix<double> > >; reference = Eigen::BiCGSTAB<Eigen::SparseMatrix<double> >&]’
/usr/include/c++/12.2.0/bits/stl_vector.h:1294:21: required from ‘void std::vector<_Tp, _Alloc>::push_back(value_type&&) [with _Tp = Eigen::BiCGSTAB<Eigen::SparseMatrix<double> >; _Alloc = std::allocator<Eigen::BiCGSTAB<Eigen::SparseMatrix<double> > >; value_type = Eigen::BiCGSTAB<Eigen::SparseMatrix<double> >]’
main.cpp:9:18: required from here
/usr/include/c++/12.2.0/bits/new_allocator.h:175:11: error: use of deleted function ‘Eigen::BiCGSTAB<Eigen::SparseMatrix<double> >::BiCGSTAB(const Eigen::BiCGSTAB<Eigen::SparseMatrix<double> >&)’
175 | { ::new((void *)__p) _Up(std::forward<_Args>(__args)...); }
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /usr/include/eigen3/Eigen/IterativeLinearSolvers:42,
from /usr/include/eigen3/Eigen/Sparse:31,
from /usr/include/eigen3/Eigen/Eigen:2:
/usr/include/eigen3/Eigen/src/IterativeLinearSolvers/BiCGSTAB.h:158:7: note: ‘Eigen::BiCGSTAB<Eigen::SparseMatrix<double> >::BiCGSTAB(const Eigen::BiCGSTAB<Eigen::SparseMatrix<double> >&)’ is implicitly deleted because the default definition would be ill-formed:
158 | class BiCGSTAB : public IterativeSolverBase<BiCGSTAB<_MatrixType,_Preconditioner> >
| ^~~~~~~~
/usr/include/eigen3/Eigen/src/IterativeLinearSolvers/BiCGSTAB.h:158:7: error: use of deleted function ‘Eigen::IterativeSolverBase<Eigen::BiCGSTAB<Eigen::SparseMatrix<double> > >::IterativeSolverBase(const Eigen::IterativeSolverBase<Eigen::BiCGSTAB<Eigen::SparseMatrix<double> > >&)’
In file included from /usr/include/eigen3/Eigen/IterativeLinearSolvers:38:
/usr/include/eigen3/Eigen/src/IterativeLinearSolvers/IterativeSolverBase.h:143:7: note: ‘Eigen::IterativeSolverBase<Eigen::BiCGSTAB<Eigen::SparseMatrix<double> > >::IterativeSolverBase(const Eigen::IterativeSolverBase<Eigen::BiCGSTAB<Eigen::SparseMatrix<double> > >&)’ is implicitly deleted because the default definition would be ill-formed:
143 | class IterativeSolverBase : public SparseSolverBase<Derived>
| ^~~~~~~~~~~~~~~~~~~
/usr/include/eigen3/Eigen/src/IterativeLinearSolvers/IterativeSolverBase.h:143:7: error: use of deleted function ‘Eigen::SparseSolverBase<Eigen::BiCGSTAB<Eigen::SparseMatrix<double> > >::SparseSolverBase(const Eigen::SparseSolverBase<Eigen::BiCGSTAB<Eigen::SparseMatrix<double> > >&)’
In file included from /usr/include/eigen3/Eigen/SparseCore:64,
from /usr/include/eigen3/Eigen/Sparse:26:
/usr/include/eigen3/Eigen/src/SparseCore/SparseSolverBase.h:67:7: note: ‘Eigen::SparseSolverBase<Eigen::BiCGSTAB<Eigen::SparseMatrix<double> > >::SparseSolverBase(const Eigen::SparseSolverBase<Eigen::BiCGSTAB<Eigen::SparseMatrix<double> > >&)’ is implicitly deleted because the default definition would be ill-formed:
67 | class SparseSolverBase : internal::noncopyable
| ^~~~~~~~~~~~~~~~
/usr/include/eigen3/Eigen/src/SparseCore/SparseSolverBase.h:67:7: error: ‘Eigen::internal::noncopyable::noncopyable(const Eigen::internal::noncopyable&)’ is private within this context
In file included from /usr/include/eigen3/Eigen/Core:162:
/usr/include/eigen3/Eigen/src/Core/util/Meta.h:424:21: note: declared private here
424 | EIGEN_DEVICE_FUNC noncopyable(const noncopyable&);
| ^~~~~~~~~~~
In file included from /usr/include/c++/12.2.0/vector:63,
from /usr/include/c++/12.2.0/functional:62,
from /usr/include/eigen3/Eigen/Core:85:
/usr/include/c++/12.2.0/bits/stl_uninitialized.h: In instantiation of ‘constexpr bool std::__check_constructible() [with _ValueType = Eigen::BiCGSTAB<Eigen::SparseMatrix<double> >; _Tp = Eigen::BiCGSTAB<Eigen::SparseMatrix<double> >&&]’:
/usr/include/c++/12.2.0/bits/stl_uninitialized.h:182:4: required from ‘_ForwardIterator std::uninitialized_copy(_InputIterator, _InputIterator, _ForwardIterator) [with _InputIterator = move_iterator<Eigen::BiCGSTAB<Eigen::SparseMatrix<double> >*>; _ForwardIterator = Eigen::BiCGSTAB<Eigen::SparseMatrix<double> >*]’
/usr/include/c++/12.2.0/bits/stl_uninitialized.h:372:37: required from ‘_ForwardIterator std::__uninitialized_copy_a(_InputIterator, _InputIterator, _ForwardIterator, allocator<_Tp>&) [with _InputIterator = move_iterator<Eigen::BiCGSTAB<Eigen::SparseMatrix<double> >*>; _ForwardIterator = Eigen::BiCGSTAB<Eigen::SparseMatrix<double> >*; _Tp = Eigen::BiCGSTAB<Eigen::SparseMatrix<double> >]’
/usr/include/c++/12.2.0/bits/stl_uninitialized.h:397:2: required from ‘_ForwardIterator std::__uninitialized_move_if_noexcept_a(_InputIterator, _InputIterator, _ForwardIterator, _Allocator&) [with _InputIterator = Eigen::BiCGSTAB<Eigen::SparseMatrix<double> >*; _ForwardIterator = Eigen::BiCGSTAB<Eigen::SparseMatrix<double> >*; _Allocator = allocator<Eigen::BiCGSTAB<Eigen::SparseMatrix<double> > >]’
/usr/include/c++/12.2.0/bits/vector.tcc:487:3: required from ‘void std::vector<_Tp, _Alloc>::_M_realloc_insert(iterator, _Args&& ...) [with _Args = {Eigen::BiCGSTAB<Eigen::SparseMatrix<double, 0, int>, Eigen::DiagonalPreconditioner<double> >}; _Tp = Eigen::BiCGSTAB<Eigen::SparseMatrix<double> >; _Alloc = std::allocator<Eigen::BiCGSTAB<Eigen::SparseMatrix<double> > >; iterator = std::vector<Eigen::BiCGSTAB<Eigen::SparseMatrix<double> > >::iterator]’
/usr/include/c++/12.2.0/bits/vector.tcc:123:21: required from ‘std::vector<_Tp, _Alloc>::reference std::vector<_Tp, _Alloc>::emplace_back(_Args&& ...) [with _Args = {Eigen::BiCGSTAB<Eigen::SparseMatrix<double, 0, int>, Eigen::DiagonalPreconditioner<double> >}; _Tp = Eigen::BiCGSTAB<Eigen::SparseMatrix<double> >; _Alloc = std::allocator<Eigen::BiCGSTAB<Eigen::SparseMatrix<double> > >; reference = Eigen::BiCGSTAB<Eigen::SparseMatrix<double> >&]’
/usr/include/c++/12.2.0/bits/stl_vector.h:1294:21: required from ‘void std::vector<_Tp, _Alloc>::push_back(value_type&&) [with _Tp = Eigen::BiCGSTAB<Eigen::SparseMatrix<double> >; _Alloc = std::allocator<Eigen::BiCGSTAB<Eigen::SparseMatrix<double> > >; value_type = Eigen::BiCGSTAB<Eigen::SparseMatrix<double> >]’
main.cpp:9:18: required from here
/usr/include/c++/12.2.0/bits/stl_uninitialized.h:90:56: error: static assertion failed: result type must be constructible from input type
90 | static_assert(is_constructible<_ValueType, _Tp>::value,
| ^~~~~
/usr/include/c++/12.2.0/bits/stl_uninitialized.h:90:56: note: ‘std::integral_constant<bool, false>::value’ evaluates to false
I'm using Eigen 3.4 and g++ version 12.2.
Any ideas how to fix this?

Answer 1

Turning my comments into a proper answer:
After looking at the code, I found that BiCGSTAB like all solvers inherits from a base class designed to prevent copying, and by extension moving, too: class SparseSolverBase : internal::noncopyable
The exact reasons for this design choice I cannot tell. If I had to guess, I'd say some solvers probably use self-referential attributes (holding pointers to other members) which would break especially with fixed-size matrices. Or using Eigen::Map may cause issues on copy, especially copy-assignment.
std::vector only works with moveable types as it needs to move when it reallocates. Even when calling reserve() beforehand, the code still needs to compile, even if it is never executed.
Three workarounds come to mind:
Use std::deque. It provides a superset of all methods that vector has but its implementation means that as long as you only call emplace_back or emplace_front and not e.g. insert, it does not need moveable types. The downside is that it is a bit slower on all individual accesses
Use std::vector<std::unique_ptr<Solver>>. Less efficient than the deque but now you can also insert, reshuffle, etc.
Use std::unique_ptr<Solver[]> and use the good old new Solver[count] allocation. Starting with C++14, you can use std::make_unique<Solver[]>(count). This has the least overhead, even less than vector but the interface isn't as nice (you can use the [index] operator but the pointer doesn't even know the array size) and the number is fixed after allocation