Reduction operations¶

Overview¶

MPL supports various communication operations that perform a reduction operation over all processes within a communicator. The reduction operation is passed as an argument to the communicator class method that realizes to communication operation. The reduction operation can be given by a user-defined two-arguments functor class, a lambda function, e.g.,

comm.reduce([](auto a, auto b) { return a + b; }, ...);

or by any of the template classes as documented below.

Class documentation¶

Maximum¶

Perform the reduction operation

\[y = \max (x_1, x_2)\]

template<typename T> struct max¶

Function object for calculating the maximum of two values in reduction operations as communicator::reduce.

Template Parameters:: T – data type of the reduction operation’s arguments and its result

Public Functions

inline T operator()(const T &x, const T &y) const¶

Parameters:

x – first argument
y – second argument

Returns:

maximum of the two arguments

Minimum¶

Perform the reduction operation

\[y = \min (x_1, x_2)\]

template<typename T> struct min¶

Function object for calculating the minimum of two values in reduction operations as communicator::reduce.

Template Parameters:: T – data type of the reduction operation’s arguments and its result

Public Functions

inline T operator()(const T &x, const T &y) const¶

Parameters:

x – first argument
y – second argument

Returns:

minimum of the two arguments

Addition¶

Perform the reduction operation

\[y = x_1 + x_2\]

template<typename T> struct plus¶

Function object for calculating the sum of two values in reduction operations as communicator::reduce.

Template Parameters:: T – data type of the reduction operation’s arguments and its result

Public Functions

inline T operator()(const T &x, const T &y) const¶

Parameters:

x – first argument
y – second argument

Returns:

sum of the two arguments

Multiplication¶

Perform the reduction operation

\[y = x_1 \cdot x_2\]

template<typename T> struct multiplies¶

Function object for calculating the product of two values in reduction operations as communicator::reduce.

Template Parameters:: T – data type of the reduction operation’s arguments and its result

Public Functions

inline T operator()(const T &x, const T &y) const¶

Parameters:

x – first argument
y – second argument

Returns:

product of the two arguments

Logical conjunction¶

Perform the reduction operation

\[y = x_1 \land x_2\]

template<typename T> struct logical_and¶

Function object for calculating the logical conjunction of two values in reduction operations as communicator::reduce.

Template Parameters:: T – data type of the reduction operation’s arguments and its result

Public Functions

inline T operator()(const T &x, const T &y) const¶

Parameters:

x – first argument
y – second argument

Returns:

logical conjunction of the two arguments

Logical disjunction¶

Perform the reduction operation

\[y = x_1 \lor x_2\]

template<typename T> struct logical_or¶

Function object for calculating the logical (inclusive) disjunction of two values in reduction operations as communicator::reduce.

Template Parameters:: T – data type of the reduction operation’s arguments and its result

Public Functions

inline T operator()(const T &x, const T &y) const¶

Parameters:

x – first argument
y – second argument

Returns:

logical (inclusive) disjunction of the two arguments

Exclusive disjunction¶

Perform the reduction operation

\[y = x_1 \oplus x_2\]

template<typename T> struct logical_xor¶

Function object for calculating the logical exclusive disjunction of two values in reduction operations as communicator::reduce.

Template Parameters:: T – data type of the reduction operation’s arguments and its result

Public Functions

inline T operator()(const T &x, const T &y) const¶

Parameters:

x – first argument
y – second argument

Returns:

logical exclusive disjunction of the two arguments

Bitwise and¶

Perform for integer arguments the bitwise reduction operation

\[y = x_1 \land x_2\]

template<typename T> struct bit_and¶

Function object for calculating the bitwise conjunction of two values in reduction operations as communicator::reduce.

Template Parameters:: T – data type of the reduction operation’s arguments and its result

Public Functions

inline T operator()(const T &x, const T &y) const¶

Parameters:

x – first argument
y – second argument

Returns:

bitwise conjunction of the two arguments

Bitwise or¶

Perform for integer arguments the bitwise reduction operation

\[y = x_1 \lor x_2\]

template<typename T> struct bit_or¶

Function object for calculating the bitwise (inclusive) disjunction of two values in reduction operations as communicator::reduce.

Template Parameters:: T – data type of the reduction operation’s arguments and its result

Public Functions

inline T operator()(const T &x, const T &y) const¶

Parameters:

x – first argument
y – second argument

Returns:

bitwise (inclusive) disjunction of the two arguments

Bitwise exclusive-or¶

Perform for integer arguments the bitwise reduction operation

\[y = x_1 \oplus x_2\]

template<typename T> struct bit_xor¶

Function object for calculating the bitwise exclusive disjunction of two values in reduction operations as communicator::reduce.

Template Parameters:: T – data type of the reduction operation’s arguments and its result

Public Functions

inline T operator()(const T &x, const T &y) const¶

Parameters:

x – first argument
y – second argument

Returns:

bitwise exclusive disjunction of the two arguments

Operator traits¶

The application of some reduction operations can be performed more efficiently by exploiting the commutativity properties of the employed reduction operation. Partial template specializations of the class mpl::op_traits provide information about the commutativity properties of the reduction operation. Users may provide further user-defined specializations of mpl::op_traits for user-defined operators.

template<typename F> struct op_traits¶

Traits class for storing meta information about reduction operations.

Template Parameters:: F – function object type

Public Static Attributes

static bool is_commutative = false¶: Is true if reduction operation specified in the template parameter F is commutative.

template<typename T> struct op_traits<max<T>>¶

Specialization of traits class op_traits for storing meta information about the max reduction operation.

Public Static Attributes

static bool is_commutative = true¶: The max reduction operation is commutative.

static bool is_commutative: Is true if reduction operation specified in the template parameter F is commutative.

template<typename T> struct op_traits<min<T>>¶

Specialization of traits class op_traits for storing meta information about the min reduction operation.

Public Static Attributes

static bool is_commutative = true¶: The min reduction operation is commutative.

static bool is_commutative: Is true if reduction operation specified in the template parameter F is commutative.

template<typename T> struct op_traits<plus<T>>¶

Specialization of traits class op_traits for storing meta information about the plus reduction operation.

Public Static Attributes

static bool is_commutative = true¶: The plus reduction operation is commutative.

static bool is_commutative: Is true if reduction operation specified in the template parameter F is commutative.

template<typename T> struct op_traits<multiplies<T>>¶

Specialization of traits class op_traits for storing meta information about the multiplies reduction operation.

Public Static Attributes

static bool is_commutative = true¶: The multiplies reduction operation is commutative.

static bool is_commutative: Is true if reduction operation specified in the template parameter F is commutative.

template<typename T> struct op_traits<logical_and<T>>¶

Specialization of traits class op_traits for storing meta information about the logical_and reduction operation.

Public Static Attributes

static bool is_commutative = true¶: The logical_and reduction operation is commutative.

static bool is_commutative: Is true if reduction operation specified in the template parameter F is commutative.

template<typename T> struct op_traits<logical_or<T>>¶

Specialization of traits class op_traits for storing meta information about the logical_or reduction operation.

Public Static Attributes

static bool is_commutative = true¶: The logical_or reduction operation is commutative.

static bool is_commutative: Is true if reduction operation specified in the template parameter F is commutative.

template<typename T> struct op_traits<logical_xor<T>>¶

Specialization of traits class op_traits for storing meta information about the logical_xor reduction operation.

Public Static Attributes

static bool is_commutative = true¶: The logical_xor reduction operation is commutative.

static bool is_commutative: Is true if reduction operation specified in the template parameter F is commutative.

template<typename T> struct op_traits<bit_and<T>>¶

Specialization of traits class op_traits for storing meta information about the bit_and reduction operation.

Public Static Attributes

static bool is_commutative = true¶: The bit_and reduction operation is commutative.

static bool is_commutative: Is true if reduction operation specified in the template parameter F is commutative.

template<typename T> struct op_traits<bit_or<T>>¶

Specialization of traits class op_traits for storing meta information about the bit_or reduction operation.

Public Static Attributes

static bool is_commutative = true¶: The bit_or reduction operation is commutative.

static bool is_commutative: Is true if reduction operation specified in the template parameter F is commutative.

template<typename T> struct op_traits<bit_xor<T>>¶

Specialization of traits class op_traits for storing meta information about the bit_xor reduction operation.

Public Static Attributes

static bool is_commutative = true¶: The bit_xor reduction operation is commutative.

static bool is_commutative: Is true if reduction operation specified in the template parameter F is commutative.