I found the following way that makes the warning message [-Wmissing-braces]
disappear.
Instead of using the instruction provided in the *block_linear_operator.h*
* block_operator<2, 2, BlockVector<double>>({op_a00, op_a01, op_a10,
op_a11});*
We can declare the block_operator the way below:
const std::array<std::array<dealii::LinearOperator<dealii::Vector<double>,
dealii::Vector<double>,
dealii::internal::LinearOperatorImplementation::EmptyPayload>,
2>, 2>
ops = {{
{{ op_uMuT, op_uMdT }},
{{ op_dMuT, op_dMdT }}
}};
const auto op_zT_wMwT_z = block_operator<2, 2, BlockVector<double>>(ops);
This way, the warning message will disappear during the compilation.
Best,
Tao
On Wednesday, March 25, 2026 at 3:04:00 PM UTC-4 Tao Jin wrote:
> Hi Wolfgang,
>
> Thanks for your reply. I dug into the dealii source code and here is what
> I found.
>
> Below is the instruction for the constructor
> /**
> * @relatesalso BlockLinearOperator
> *
> * A variant of above function that encapsulates a given collection @p ops
> of
> * LinearOperators into a block structure. Here, it is assumed that Range
> and
> * Domain are block vectors, i.e., derived from
> * @ref BlockVectorBase.
> * The individual linear operators in @p ops must act on the underlying
> vector
> * type of the block vectors, i.e., on Domain::BlockType yielding a result
> in
> * Range::BlockType.
> *
> * The list @p ops is best passed as an initializer list. Consider for
> example
> * a linear operator block (acting on Vector<double>)
> * @code
> * op_a00 | op_a01
> * |
> * ---------------
> * |
> * op_a10 | op_a11
> * @endcode
> * The corresponding block_operator invocation takes the form
> * @code
>
> * * block_operator<2, 2, BlockVector<double>>({op_a00, op_a01, op_a10,
> op_a11});* * @endcode
> *
> * @ingroup LAOperators
> */
>
> I followed the above instruction but still got the same warning message
> during compilation.
>
> Also, in the source code (*block_linear_operator.h*)
>
> https://dealii.org/current/doxygen/deal.II/block__linear__operator_8h_source.html
>
> On line 665 there is a *TODO* tag:
> // TODO: Create block payload so that this can be initialized correctly
> BlockLinearOperator<Range, Domain, BlockPayload>
> <https://dealii.org/current/doxygen/deal.II/classBlockLinearOperator.html#ad2533970716e61d8476d73b5977d1d89>
>
> return_op{BlockPayload()};
>
> I wonder whether this is the reason for the warning message. (Sorry that
> my C++ skill is not good enough to fix this myself since the
> block_linear_operator seems to be a quite complex class).
>
> Best,
>
> Tao
>
>
> On Wednesday, March 25, 2026 at 12:04:28 PM UTC-4 Wolfgang Bangerth wrote:
>
>> On 3/24/26 19:27, Tao Jin wrote:
>> >
>> > I tried to place some extra curly braces but the warining message is
>> still there.
>> >
>> > Does anyone have any idea how to get rid of the warning message?
>>
>> Sometimes it takes two more levels of braces. Alternatively, look up what
>> the
>> type of the constructor argument is and construct that explicitly, rather
>> than
>> in-place.
>>
>> Best
>> Wolfgang
>>
>
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