Algorithm Update

This section lists all the algorithms that can handle execution policy parameter. It further looks at the usage of the Run and Measure function.

We'll cover the following

Execution Policy Parameter

The execution policy parameter was added to most of the existing algorithms.

Here’s the list:

adjacent_difference inplace_merge replace_copy
adjacent_find is_heap replace_copy_if
all_of is_heap_until replace_if
any_of is_partitioned reverse
copy is_sorted reverse_copy
copy_if is_sorted rotate
copy_n is_sorted_until rotate_copy
count lexicographical_compare search
count_if max_element search_n
equal merge set_difference
exclusive_scan min_element set_intersection
fill minmax_element set_symmetric_difference
fill_n mismatch set_union
find move sort
find_end none_of stable_partition
find_first_of nth_element stable_sort
find_if partial_sort swap_ranges
find_if_not partial_sort_copy transform
for_each partition transform_exclusive_scan
for_each_n partition_copy transform_inclusive_scan
generate remove transform_reduce
generate_n remove_copy uninitialized_copy
includes remove_copy_if uninitialized_copy_n
inclusive_scan remove_if uninitialized_fill
inner_product replace uninitialized_fill_n
unique unique_copy

New Algorithms

To fully support new parallel execution patterns The Standard Library was also equipped with a set of new algorithms:

Algorithm Description
for_each similar to for_each except returns void
for_each_n applies a function object to the first n elements of a sequence
reduce similar to accumulate, except out of order execution to allow parallelism
transform_reduce transforms the input elements using a unary operation, then reduces the output out of order
exclusive_scan parallel version of partial_sum, excludes the i-th input element from the i-th sum, out of order execution to allow parallelism
inclusive_scan parallel version of partial_sum, includes the i-th input element in the i-th sum, out of order execution to allow parallelism
transform_exclusive_scan applies a functor, then calculates exclusive scan
transform_inclusive_scan applies a functor, then calculates inclusive scan

The new algorithms form three groups: for_each, reduce and then scan, plus their alternatives.

With reduce and scan you also get “fused” versions like transform_reduce. These compositions should give you much better performance than using two separate steps - because the cost of parallel execution setup is smaller and also you have less one loop traversals.

The new algorithms also provide overloads withou​t the execution policy parameter so that you can use them in a standard serial version.

In the next lesson, you’ll find a description of each group.

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