Function utils::mpiPartitionRange

Function Documentation

inline auto utils::mpiPartitionRange(const unsigned long rangeStart, const unsigned long rangeEnd) -> std::pair<unsigned long, unsigned long>

Divide a contiguous trial-number range evenly across every MPI rank.

Splits [rangeStart, rangeEnd) into mpiSize() contiguous sub-ranges, as evenly as possible: with total = rangeEnd - rangeStart, base = total / mpiSize() trials go to every rank, and the first (total % mpiSize()) ranks each get one additional trial, so the sub-ranges’ own sizes add up to exactly total regardless of whether it divides evenly. When mpiSize() == 1 (including every build not compiled with SLUG_MPI), this always returns {rangeStart, rangeEnd} unchanged.

Parameters:

  • rangeStart – Start of the range to divide (inclusive)

  • rangeEnd – End of the range to divide (exclusive)

Returns:

The [start, end) sub-range of [rangeStart, rangeEnd) that this process’s own rank should run – every rank’s own returned sub-range is disjoint from every other rank’s, and their union is exactly [rangeStart, rangeEnd), so trial numbers themselves never collide across ranks (only unique IDs need mpiUidStride for that – see its own comment)