Instantiation problem for Utilities::MPI::sum (const ArrayView< const T > &values, const MPI_Comm &mpi_communicator, const ArrayView< T > &sums)

[Feimi Yu]

Hi,

I was trying to use the the function Utilities::MPI::sum (const ArrayView< const T > &values, const MPI_Comm &mpi_communicator, const ArrayView< T > &sums)

for an std::vector<int>. I created an ArrayView<int> to pack the vector and passed it into this function. However, the compiler keeps telling me:

undefined reference to 'void dealii::Utilities::MPI::sum<dealii::ArrayView<int>, dealii::ArrayView<int> >(dealii::ArrayView<int> const&, ompi_communicator_t* const&, dealii::ArrayView<int>&)'

I checked base/mpi.inst.in and cmake/config/template-arguments.in. Int type should be included in the instantiation list, but I could not figure out why this does not work for me.

Thanks!

Feimi

[Jean-Paul Pelteret]

Dear Feimi,

On first glance, it looks like the object you send in as the first argument to this function has the wrong type. The function expects an ArrayView< const int >, but you are passing it an ArrayView< int >. That’s the first thing that I spotted, but hopefully its just this that’s an issue for you.

I hope that this helps.

Best,

Jean-Paul

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[Feimi Yu]

Hi Jean-Paul,

Thanks for your reply!

Yes, I did try passing an ArrayView<const int>, with no luck. I was told the same undefined reference thing.

Feimi

On Tuesday, January 28, 2020 at 1:53:35 AM UTC-5, Jean-Paul Pelteret wrote:

Dear Feimi,

On first glance, it looks like the object you send in as the first argument to this function has the wrong type. The function expects an ArrayView< const int >, but you are passing it an ArrayView< int >. That’s the first thing that I spotted, but hopefully its just this that’s an issue for you.

I hope that this helps.

Best,

Jean-Paul

On 27 Jan 2020, at 19:42, Feimi Yu <yuf...@gmail.com> wrote:

Hi,

I was trying to use the the function Utilities::MPI::sum (const ArrayView< const T > &values, const MPI_Comm &mpi_communicator, const ArrayView< T > &sums)

for an std::vector<int>. I created an ArrayView<int> to pack the vector and passed it into this function. However, the compiler keeps telling me:

undefined reference to 'void dealii::Utilities::MPI::sum<dealii::ArrayView<int>, dealii::ArrayView<int> >(dealii::ArrayView<int> const&, ompi_communicator_t* const&, dealii::ArrayView<int>&)'

I checked base/mpi.inst.in and cmake/config/template-arguments.in. Int type should be included in the instantiation list, but I could not figure out why this does not work for me.

Thanks!

Feimi

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[Feimi Yu]

I uploaded a minimal code to reproduce the problem I encountered.

Thanks!

Feimi

[Bruno Turcksin]

Feimi,

You need to have two different ArrayView. It won't work with a single ArrayView. The input one (values) need to be an ArrayView<const int> and the output one (sum) an ArrayView<int>.

Best,

Bruno

[Feimi Yu]

Hi Bruno,

Thanks for your reply!

That's not true. The input and output arrays may be the same as described in the documentation. The template instatiation error does not check whether they are the same, either.

In addition, two different arrays give the same error.

Feimi

[Daniel Arndt]

Feimi,

it's picking the wrong overload.

Utilities::MPI::sum(local_vector, mpi_communicator, local_vector);

works as well as

Utilities::MPI::sum<int>(my_view, mpi_communicator, my_view);

Best,

Daniel

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[Feimi Yu]

Hi Daniel,

Thanks for the solution!

From my understanding, it's picking

template<typename T, typename U>

void sum(const T &values, const MPI_Comm &mpi_communicator, U &sums)

instead of

template<typename T>

void sum(const ArrayView<const T> &values, const MPI_Comm & mpi_communicator, const ArrayView<T> & sums)

And that's why it is complaining that "<ArrayView<int const>, ArrayView<int>>" is not instantiated for the first one. Am I correct?

Now I understand that directly passing the vector works. And to have the second one working, I need to explicitly tell the compiler which one to use, like:

Utilities::MPI::sum<int>(my_view, mpi_communicator, my_view);

Just tested with that and it compiled & ran normally.

Thanks!

Feimi

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