HPL_reduce(3)

💖 HPL_reduce(3) — the HPL Library Functions era 💖

okay bestie, sit down, hydrate, and let me tell you about HPL_reduce — literally one of the HPL Library Functions and honestly? she's giving reduce operation. that's it, that's the whole NAME section, no notes 💅

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✨ SYNOPSIS ✨

#include "hpl.h"

int HPL_reduce( void * BUFFER, const int COUNT, const HPL_T_TYPE DTYPE,
const HPL_T_OP OP, const int ROOT, MPI_Comm COMM );

look at her. six arguments. main character energy fr fr 👑

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🌸 DESCRIPTION 🌸

so HPL_reduce does a global reduce operation across all processes of a group. slay. that's the job. that's what she does.

but here's the part you gotta hear, bestie — the input buffer is used as a workarray. which means in all processes but the accumulating process, your original data gets corrupted. 😭 not a vibe, just a fact. she's destructive like that. lowkey iconic, highkey dangerous.

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🎀 ARGUMENTS 🎀

• BUFFER (local input/output) void * — on entry, BUFFER points to the buffer to be reduced. on exit, and in the process of rank ROOT, this array holds the reduced data 💖. this buffer is also used as workspace during the operation in the other processes of the group, iykyk.
• COUNT (global input) const int — on entry, COUNT tells you the number of entries in BUFFER. and bestie, COUNT must be at least zero. no negative counts, we don't do that here 🙈.
• DTYPE (global input) const HPL_T_TYPE — on entry, DTYPE specifies the type of the buffers operands. the type! of the operands! of the buffers! ✨
• OP (global input) const HPL_T_OP — on entry, OP is a pointer to the local combine function. she's the one doing the combining. the girlboss of the operation 🫶.
• ROOT (global input) const int — on entry, ROOT is the coordinate of the accumulating process. that's the one process keeping the data. the chosen one. the main character 🌟.
• COMM (global/local input) MPI_Comm — the MPI communicator identifying the process collection. the group chat, basically 💬.

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🦋 SEE ALSO 🦋

• HPL_broadcast (3)
• HPL_all_reduce (3)
• HPL_barrier (3)
• HPL_min (3)
• HPL_max (3)
• HPL_sum (3)

go read those too, they're all serving 🌈

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heads up bestie: that buffer-as-workarray thing means your original data in every process except ROOT is gone-gone after this call. not corrupted-and-recoverable. corrupting. periodt. 💀

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and that's the whole page, bestie!! this one shipped with HPL 2.2 and was dated February 24, 2016 🎀 — yeah she's an elder but she still ate. mwah, stan, bye 💖✨🦋