Internal deal.II error when instantiating TrilinosWrappers::block_operator

[Lucas Myers]

Hi folks,

I'm trying to use the block_operator technique on Trilinos vectors and matrices, but I can't quite get it to compile. For simplicity, the relevant lines of code are:

```

#include <deal.II/lac/linear_operator_tools.h>
#include <deal.II/lac/trilinos_linear_operator.h>

using vec = dealii::LinearAlgebraTrilinos::MPI::Vector;

using block_vec = dealii::LinearAlgebraTrilinos::MPI::BlockVector;

const auto B = dealii::TrilinosWrappers::linear_operator<vec, vec>(system_matrix.block(0, 0));

const auto P_inv = dealii::TrilinosWrappers::block_operator<1, 1, block_vec>({B});

```

where system_matrix is of type `dealii::LinearAlgebraTrilinos::MPI::BlockSparseMatrix`.

The first error that comes up looks like:

`deal.II/lac/block_linear_operator.h:679:37: error: ‘populate_linear_operator_functions’ was not declared in this scope; did you mean ‘dealii::internal::BlockLinearOperatorImplementation::populate_linear_operator_functions’?`

Is this a bug in deal.II? That would be my first inclination, given that I cannot see how it would be template-related.

There are a few other errors that come up, so I'm attaching the error message in a text file. 

Any tips on debugging this? I'm finding the compiler output basically inscrutable. Any help is appreciated, so sorry for all the spam!

- Lucas

[Wolfgang Bangerth]

Lucas:

> I'm trying to use the block_operator technique on Trilinos vectors and
> matrices, but I can't quite get it to compile. For simplicity, the relevant
> lines of code are:
> ```
> #include <deal.II/lac/linear_operator_tools.h>
> #include <deal.II/lac/trilinos_linear_operator.h>
>
> using vec = dealii::LinearAlgebraTrilinos::MPI::Vector;
> using block_vec = dealii::LinearAlgebraTrilinos::MPI::BlockVector;
> const auto B = dealii::TrilinosWrappers::linear_operator<vec,
> vec>(system_matrix.block(0, 0));
> const auto P_inv = dealii::TrilinosWrappers::block_operator<1, 1, block_vec>({B});
> ```
> where system_matrix is of type
> `dealii::LinearAlgebraTrilinos::MPI::BlockSparseMatrix`.
>
> The first error that comes up looks like:
>
> `deal.II/lac/block_linear_operator.h:679:37: error:
> ‘populate_linear_operator_functions’ was not declared in this scope; did you
> mean
> ‘dealii::internal::BlockLinearOperatorImplementation::populate_linear_operator_functions’?`
>
> Is this a bug in deal.II?

Perhaps. I don't know the LinearOperator framework well, and so don't quite
know what to suggest -- I hope that someone else might chime in.

Is the code above all you actually need?

Best
W.

--
------------------------------------------------------------------------
Wolfgang Bangerth email: bang...@colostate.edu
www: http://www.math.colostate.edu/~bangerth/

[Luca Heltai]

Dear Lucas,

take a look at the tests directory of deal.II:

https://github.com/dealii/dealii/blob/master/tests/lac/block_linear_operator_05.cc

there are many small examples and snippets that show how to use this.

In particular, I think the problem is in the fact that you are calling directly dealii::TrilinosWrappers::linear_operator and dealii::TrilinosWrappers::block_operator.

These are used internally by the functions in linear_operator_tools, and, btw, you are not required to include

#include <deal.II/lac/trilinos_linear_operator.h>

as these are included by linear_operator_tools.h, and the typical usage is through the functions dealii::linear_operator, dealii::block_operator, dealii::block_diagonal_operator, etc. (notice these are in dealii namespace, not in dealii::TrilinosWrappers namespace).

e.g., this should compile:

using vec = dealii::LinearAlgebraTrilinos::MPI::Vector;
using block_vec = dealii::LinearAlgebraTrilinos::MPI::BlockVector;

const auto B = linear_operator<vec>(system_matrix.block(0, 0)); // Notice this is not dealii::TrilinosWrappers::linear_operator
const auto P_inv = block_diagonal_operator<1, block_vec >(std::array<decltype(B), 1>({{B}}));

Creating (as for your example) a block operator with a single block.

L.

Ps: I don’t see an obvious reason why your example should not compile too. Could you try to modify

https://github.com/dealii/dealii/blob/master/tests/lac/block_linear_operator_05.cc

to reflect your example, and open an issue with a MWE that fails to compile? Reading your code, I would have expected it to compile, and I think you have spotted a problem in deal.II due to an unusual way in which you are using the code.

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> <linear_operator_bug.txt>