[Andrea_85]

Hi All,

Do min and max function work for scalarField? something like

scalar xMin = min(myScalarField);
scalar xMax = max(myScalarField);

Do they work also in parallel?
I need to calcualte the minimum and maximum value of a vector during a parallel simulation and use them for some calculations. I got different values when using or not the "reduce" command on xMin and xMax and it looks like i get the correct values when "reduce" is not used. I am a bit confused.

Which is the best/correct way to calculate minimum and maximum value of a scalarField during a parallel run?

Thanks

Andrea

[alexeym]

Hi,

if you just use min or max you get minimum/maximum on a processor. In case of serial run you've got one process, so value is unique. In case of parallel run you can either use gMax/gMin functions (they do reduce thing for you), or first do min/max to get minimum/maximum on a processor and then do reduce to get minimum/maximum of all processors.

[Andrea_85]

Hi Alexey,

thank you for interesting in my post.
Which is the correct sintax for the reduce operations? Something like

reduce(xMin, minOp<scalar>());
reduce(xMax, maxOp<scalar>());

i will also try with gmax/gmin...

thanks again

andrea

[alexeym]

Well, if you take a look at src/OpenFOAM/fields/Fields/Field/FieldFunctions.C

#define G_UNARY_FUNCTION(ReturnType, gFunc, Func, rFunc)                      \
                                                                              \
template<class Type>                                                          \
ReturnType gFunc(const UList<Type>& f, const int comm)                        \
{                                                                             \
    ReturnType res = Func(f);                                                 \
    reduce(res, rFunc##Op<Type>(), Pstream::msgType(), comm);                 \
    return res;                                                               \
}                                                                             \
TMP_UNARY_FUNCTION(ReturnType, gFunc)
    
G_UNARY_FUNCTION(Type, gMax, max, max)
G_UNARY_FUNCTION(Type, gMin, min, min)

so gMax will be preprocessed into

template<class Type>
Type gMax(const UList<Type>& f, const int comm)
{
    Type res = max(f);
    reduce(res, maxOp<type>(), Pstream::msgType(), comm);
    return res;
}
...

so, yes, for scalar field reduce call will be

reduce(xMax, maxOp<scalar>());