Maybe typo on Step-40's webpage

[Zhidong Brian Zhang]

Dear, Colleagues,

I tried to run the code from Step-40's webpage,
https://www.dealii.org/current/doxygen/deal.II/step_40.html

However, I encountered errors: error: ‘LinearAlgebraPETSc’ is not a namespace-name

   using namespace ::LinearAlgebraPETSc;

So I compared the code from the locally installed file of Step-40 and found there is a slight difference:

Webpage:

namespace LA
{
#if defined(DEAL_II_WITH_PETSC) && !defined(DEAL_II_PETSC_WITH_COMPLEX) && \
!(defined(DEAL_II_WITH_TRILINOS) && defined(FORCE_USE_OF_TRILINOS))
using namespace ::LinearAlgebraPETSc;
# define USE_PETSC_LA
#elif defined(DEAL_II_WITH_TRILINOS)
using namespace ::LinearAlgebraTrilinos;
#else
# error DEAL_II_WITH_PETSC or DEAL_II_WITH_TRILINOS required
#endif
} // namespace LA

Locally installed:

namespace LA
{
#if defined(DEAL_II_WITH_PETSC) && !defined(DEAL_II_PETSC_WITH_COMPLEX) && \
  !(defined(DEAL_II_WITH_TRILINOS) && defined(FORCE_USE_OF_TRILINOS))
  using namespace dealii::LinearAlgebraPETSc;
#  define USE_PETSC_LA
#elif defined(DEAL_II_WITH_TRILINOS)
  using namespace dealii::LinearAlgebraTrilinos;
#else
#  error DEAL_II_WITH_PETSC or DEAL_II_WITH_TRILINOS required
#endif
} // namespace LAEnter code here...

I have highlighted the difference. After adding "dealii", the program can be run successfully.

I guess maybe these are typos. I am new to deal.ii, so I am not sure my guess is correct or not. I am just curious about this (no offence), because I may miss some important point here.

Thank you very much for your attention!

Zhidong Brian Zhang

[David Wells]

Dear Zhidong,

Thanks for finding and reporting this :)

When we compile the doxygen documentation we remove all occurrences of

dealii::

since, for a variety of reasons, it's easier to pretend in the manual
that all deal.II classes are in the global namespace. This is done
with, if I recall correctly, a simple text substitution - hence, the
webpage for step-40 has

using namespace ::LinearAlgebraPETSc

instead of what is actually in the source file:

using namespace dealii::LinearAlgebraPETSc

Put another way: this text substitution is wrong for this example and
needs to be fixed. Could you help us by opening a GitHub issue to
track this problem with the documentation?

Thanks,
David

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[Zhidong Brian Zhang]

Dear, David,

Thank you very much for your timely reply!

Now it is clear. It is so important to double check with experts of deal.ii.

I already opened a GitHub issue: https://github.com/dealii/dealii/issues/9163

Thanks

Best regards,

Zhidong Brian Zhang

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