Reductions

Arcane allows performing the three classic types of reduction (Min, Max, and Sum) on the accelerator. There are two ways to perform reductions:

• via a classic loop RUNCOMMAND_ (Reductions via a loop)
• via a specific API (Direct Reductions)

Reductions via a loop

The classes ReducerMax2, ReducerMin2, and ReducerSum2 allow performing reductions on accelerators. They are used inside loops such as RUNCOMMAND_LOOP1() or RUNCOMMAND_ENUMERATE() or RUNCOMMAND_MAT_ENUMERATE().

First, you must declare an instance of one of the reduction classes and then pass it as an additional parameter to the loops. For example:

#include "arcane/accelerator/RunCommandEnumerate.h"
#include "arcane/accelerator/Reduce.h"
{
  Arcane::Accelerator::RunQueue queue = ...;
  auto command = makeCommand(queue);
  Arcane::Accelerator::ReducerMin2<double> minimum_reducer(command);
  Arcane::VariableCellReal my_variable = ...;
  auto in_my_variable = viewIn(command,my_variable);
  command << RUNCOMMAND_ENUMERATE(Cell,cid,allCells(),minimum_reducer)
  {
    minimum_reducer.combine(in_my_variable[cid]);
  };
  info() << "MinValue=" << minimum_reducer.reducedValue();
}

Warning

Each instance can only be used once.

It is possible to use multiple reduction instances if you want to perform several reductions at once. For example:

#include "arcane/accelerator/RunCommandEnumerate.h"
#include "arcane/accelerator/Reduce.h"
{
  Arcane::Accelerator::RunQueue queue = ...;
  auto command = makeCommand(queue);
  Arcane::Accelerator::ReducerMin2<double> minimum_reducer(command);
  Arcane::Accelerator::ReducerMax2<double> maximum_reducer(command);
  Arcane::VariableCellReal my_variable = ...;
  auto in_my_variable = viewIn(command,my_variable);
  command << RUNCOMMAND_ENUMERATE(Cell,cid,allCells(),minimum_reducer,maximum_reducer)
  {
    minimum_reducer.combine(in_my_variable[cid]);
    maximum_reducer.combine(in_my_variable[cid]);
  };
  info() << "MinValue=" << minimum_reducer.reducedValue();
  info() << "MaxValue=" << maximum_reducer.reducedValue();
}

Direct Reductions

The GenericReducer class allows launching a specific command dedicated to reduction. An instance of GenericReducer can be used multiple times.

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Usage for materials Memory Pool