Operator*= works in Step-41 but not in my program

[Xuefeng Li]

Hi, everyone!

I ran into a compiler error that feels strange to me. And I use C++ only occasionally.

/home/li/cbrc01.cc:1378:8: error: no match for ‘operator*=’ (operand types are ‘const dealii::TrilinosWrappers::MPI::Vector’ and ‘int’)
 1378 |     um *= -1;
      |     ~~~^~~~~
/home/li/share/dealii-9.6.0/include/deal.II/lac/trilinos_vector.h:1993:5: note: candidate: ‘dealii::TrilinosWrappers::MPI::Vector& dealii::TrilinosWrappers::MPI::Vector::operator*=(dealii::TrilinosScalar)’ (near match)
 1993 |     Vector::operator*=(const TrilinosScalar a)
      |     ^~~~~~
/home/li/share/dealii-9.6.0/include/deal.II/lac/trilinos_vector.h:1993:5: note:   passing ‘const dealii::TrilinosWrappers::MPI::Vector*’ as ‘this’ argument discards qualifiers
make[2]: *** [CMakeFiles/cbrc01.dir/build.make:76: CMakeFiles/cbrc01.dir/cbrc01.cc.o] Error 1
make[1]: *** [CMakeFiles/Makefile2:90: CMakeFiles/cbrc01.dir/all] Error 2
make: *** [Makefile:91: all] Error 2

According to the above error message, the compiler indeed recognized "um" to be a dealii::TrilinosWrappers::MPI::Vector object. It further suggested that it is a "near match" to the defined operator "Vector::operator*=(const TrilinosScalar a)".

Furthermore, Step-41 used exactly the same operation in method
      void ObstacleProblem<dim>::update_solution_and_constraints()
in the line
      contact_force *= -1;
I was able to compile and run Step-41 without error. That indicates that my installations of dealii and Trilinos work for the operator *=.

Your help is greatly appreciated. Thanks in advance.

Best,

X. Li

[Praveen C]

Maybe the clue is already in the error message

On 16 Feb 2025, at 8:59 AM, 'Xuefeng Li' via deal.II User Group <dea...@googlegroups.com> wrote:

/home/li/cbrc01.cc:1378:8: error: no match for ‘operator*=’ (operand types are ‘const dealii::TrilinosWrappers::MPI::Vector’ and ‘int’)
 1378 |     um *= -1;

Your um seems to be declared const in this context.

best

praveen

[Xuefeng Li]

I see. That's my newbie mistake. Thanks again for pointing out the root of the problem.

Best,

--Xuefeng Li, (504)865-3340(phone)

   Chair, Department of Mathematics and Computer Science
   Like floating clouds, the heart rests easy
   Like flowing water, the spirit stays free

      Loyola University New Orleans

   New Orleans, Louisiana (504)865-2051(fax)

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