[Shibi]

Hello to all,


I would like to know if there is a way to retrieve the a reference to the scalarField storing the cell volume of the mesh from an ldusolver.

We could call the reference to the objectRegistry with:

const objectRegistry& a =  matrix().mesh().thisDb();

And possibly get the cell volumes with the cellVolumes() function from the primitiveMesh.

But I am getting the error:

error: invalid use of incomplete type ‘const class Foam::objectRegistry’

Would appreciate the help.

[olesen]

The error means that objectRegistry was forward declared but not known completely in your code context.
Add an #include "objectRegistry.H" in your file.

Nonetheless not sure why you want to get at cell volumes in such a roundabout manner - they are directly available from the mesh - don't have to lookup from the registry.

[Shibi]

Originally Posted by olesen

The error means that objectRegistry was forward declared but not known completely in your code context.
Add an #include "objectRegistry.H" in your file.

Nonetheless not sure why you want to get at cell volumes in such a roundabout manner - they are directly available from the mesh - don't have to lookup from the registry.

Thanks for the reply.

How so?

Inside the LDU solver, how can you get access to mesh volume?

Something like:

const fvMesh* myMesh = dynamic_cast<const fvMesh*>(&matrix().mesh());
 const scalarField& V = myMesh->V();

For the above code to work, you have to:

#include "fvMesh.H"
#include "volMesh.H"

and add to Make/options

EXE_INC = \
    -I$(LIB_SRC)/lduSolvers/lnInclude  \
    -I$(LIB_SRC)/finiteVolume/lnInclude 

EXE_LIBS = \
    -llduSolvers \
    -lfiniteVolume

Or something else?




As additional information this is being made in OF2106

[dlahaye]

Replace

const scalarField& V = myMesh->V();

by

const scalarField& V = myMesh.V();

[Shibi]

Originally Posted by dlahaye

Replace

const scalarField& V = myMesh->V();

by

const scalarField& V = myMesh.V();

Not possible:

error: request for member ‘V’ in ‘myMesh’, which is of pointer type ‘const Foam::fvMesh*’ (maybe you meant to use ‘->’ ?)
   137 |     const scalarField& V = myMesh.V()

[olesen]

Originally Posted by Shibi

Not possible:

error: request for member ‘V’ in ‘myMesh’, which is of pointer type ‘const Foam::fvMesh*’ (maybe you meant to use ‘->’ ?)
   137 |     const scalarField& V = myMesh.V()

I re-read your original question. You want to somehow get volume information from the lduMesh it seems? Not sure if I've properly understood what you are trying to do. In which file (please include the path) are you attempting to hack this in?

[Shibi]

Originally Posted by olesen

I re-read your original question. You want to somehow get volume information from the lduMesh it seems? Not sure if I've properly understood what you are trying to do. In which file (please include the path) are you attempting to hack this in?

Yes. I want to get volume information from e.g., the PCG solver. the above code seems to work, although I do not know if there is a more straightforward way of doing this.

[Shibi]

Is the approach with dynamic_cast the best approach? Or is there something better?

[Shibi]

Originally Posted by dlahaye

Replace

const scalarField& V = myMesh->V();

by

const scalarField& V = myMesh.V();

To make this work I have to change:

const fvMesh* myMesh = dynamic_cast<const fvMesh*>(&matrix().mesh());

to

const fvMesh& myMesh = dynamic_cast<const fvMesh&>(matrix().mesh());

[olesen]

I would normally write it like this:

const auto* meshPtr = isA<fvMesh>(matrix().mesh());

if (!meshPtr) FatalErrorInFunction .... 

const auto& myMesh = *meshPtr;

[Shibi]

Originally Posted by olesen

I would normally write it like this:

const auto* meshPtr = isA<fvMesh>(matrix().mesh());

if (!meshPtr) FatalErrorInFunction .... 

const auto& myMesh = *meshPtr;

Hello Mr. Olesen.

Thanks for the input. It is shorter but on the background it should do the same thing: since the isA<fvMesh> function will do the casting.

template<class TargetType, class Type>
inline const TargetType* isA(const Type& t)
{
    const Type* p = &t;
    return dynamic_cast<const TargetType*>(p);
}

but I will adopt it and thank you for the conversion check.

[olesen]

Originally Posted by Shibi

Hello Mr. Olesen.

Thanks for the input. It is shorter but on the background it should do the same thing: since the isA<fvMesh> function will do the casting.
...

Yes it is exactly the same under the hood, but saves other places in OpenFOAM where we previously had a check with isA<..> followed by a refCast<...> : not really any point performing the dynamic cast twice.

The other important reason for that particular design pattern is that if you have a dynamic_cast<Type*>(...) it will return a nullptr if the casting fails, but if you use dynamic_cast<Type&>(...) it will throw a bad cast exception if the casting fails. So much easier to use the pointer version and not deal with try/catch things.

[Shibi]

One further question, if possible.

Can I create a variable as:

const fvMesh& meshRef_;

And initialize it in the constructor with a function as:

meshRef_(initMeshRef())

const Foam::fvMesh& Foam::myClass::initMeshRef() const
{
    const auto* meshPtr = isA<fvMesh>(matrix().mesh()); 
    if (!meshPtr)
    {
        FatalErrorInFunction
            << "Some Error message" << nl
            << exit(FatalError);
    }

    return *meshPtr;
}

Is this good practice? Or should I not define a reference as a class attribute ?
Sorry if this is too basic...

[olesen]

No problem and not necessarily bad style to have a const or non-const reference as a member variable. However you most certainly cannot easily or reliably do what you have written. Should either use a static method or a file-scope local function that take the matrix as a parameter and return the reference.

Take a look at this code chunk and work your way upwards to see how it's done.
https://develop.openfoam.com/Develop...rDriver.C#L139


EDIT: if you need to, please check stackoverflow, google whatever. Try a small test class where you attempt to instantiate a member variable within the declaration of the constructor by calling a member function as part of that process (ie, what you've essentially scoped out here). See how successful you are. Try with clang as well to make sure that you are not relying on any special gcc "magic" to somehow save you. If you succeed or fail, please report back. Learning by doing is the only way to convince yourself here.

[Shibi]

Originally Posted by olesen

Should either use a static method or a file-scope local function that take the matrix as a parameter and return the reference.

I did not quite understand this portion. This is to be placed inside a custom lduSolver (e.g., PBICGStab) so I should have the lduMesh reference to cast from the lduMatrix::solver.

Edit: I don't know how to use clang (is it possible to do wmake $someFlag clang?. Will it work if I compiled OF with gcc?), but the function appears to work fine. I guess that since the mesh object is unique and derived from the lduMesh that is being used to cast, there should not be a problem.