GATHER(3PVM)

🦋 GATHER(3PVM) 🦋

okay so bestie, welcome to the pvm_gather page from PVM Version 3.4 — it's giving group chat where everyone sends their lil data to the root and the root collects it into one big array. iconic 💖

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✨ NAME ✨

pvm_gather — a specified member of the group receives messages from each member of the group and gathers these messages into a single array. periodt. 💅

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💅 SYNOPSIS 💅

C:

int info = pvm_gather( void *result,  void *data,
                  int count, int datatype, int msgtag,
                  char *group, int rootginst)

Fortran:

call pvmfgather(result, data, count, datatype,
                msgtag, group, rootginst, info)

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🌸 PARAMETERS 🌸

• result — On the root, this is a pointer to the starting address of an array of datatype local values that are gonna be accumulated from the members of the group. If n is the number of members in the group, then this array of datatype should be at least length n*count. This argument is meaningful only on the root. root only, bestie. 💖
• data — For each group member, this is a pointer to the starting address of an array of length count of datatype that will be sent to the specified root member of the group. your lil contribution. ✨
• count — Integer specifying the number of elements of datatype to be sent by each member of the group to the root. how many things you're sending.
• datatype — Integer specifying the type of the entries in the result and data arrays. (See below for defined types.) the vibe of your data.
• msgtag — Integer message tag supplied by the user. msgtag should be >= 0. It lets the user's program distinguish between different kinds of messages. tag it so you know what's what. 🏷️
• group — Character string group name of an existing group. your squad's name. 👑
• rootginst — Integer instance number of the group member who performs the gather of the messages from the members of the group. the main character who collects everything. 🌟
• info — Integer status code returned by the routine. Values less than zero indicate an error. negative means something went wrong, no cap. 😭

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🔥 DESCRIPTION 🔥

pvm_gather() performs a send of messages from each member of the group to the specified root member of the group. All group members must call pvm_gather(), and each one sends its array data of length count of datatype to the root, which accumulates these messages into its result array. It's as if the root receives count elements of datatype from the *i*th member of the group and places these values in its result array starting with offset i*count from the beginning of the result array. The root task is identified by its instance number in the group. math but make it cute. ✨

C and Fortran defined datatypes are:

C datatypes   FORTRAN datatypes
-----------------------------------
PVM_BYTE       BYTE1
PVM_SHORT      INTEGER2
PVM_INT        INTEGER4
PVM_FLOAT      REAL4
PVM_CPLX       COMPLEX8
PVM_DOUBLE     REAL8
PVM_DCPLX      COMPLEX16
PVM_LONG

In using the scatter and gather routines, keep in mind that C stores multidimensional arrays in row order, typically starting with an initial index of 0; whereas Fortran stores arrays in column order, typically starting with an offset of 1. lowkey important for not messing up your arrays. 🧚

Note: pvm_gather() does not block. If a task calls pvm_gather and then leaves the group before the root has called pvm_gather, an error may occur. so don't dip early, bestie. 💀

The current algorithm is very simple and robust. A future implementation may make more efficient use of the architecture to allow greater parallelism. future glow-up pending. ⭐

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🎀 EXAMPLES 🎀

C:

info =  pvm_gather(&getmatrix, &myrow, 10, PVM_INT,
                   msgtag, "workers", rootginst);

Fortran:

CALL PVMFGATHER(GETMATRIX, MYCOLUMN, COUNT, INTEGER4,
&                MTAG, 'workers', ROOT, INFO)

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🙈 ERRORS 🙈

These error conditions can be returned by pvm_gather:

• PvmNoInst — Calling task is not in the group. you're not on the list, bestie. 😭
• PvmBadParam — The datatype specified is not appropriate. wrong vibe of data.
• PvmSysErr — Pvm system error. system said no. 💀

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🌈 SEE ALSO 🌈

• pvm_bcast(3PVM)
• pvm_barrier(3PVM)
• pvm_psend(3PVM)

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okay that's the whole page bestie, hope you slayed that gather. this was PVM Version 3.4, manual page GATHER(3PVM), dated 21 April, 1994 — periodt 💖✨🦋