---
name: "pvm_scatter"
section: "3"
platform: "linux"
package: "pvm-dev"
version: "3.4.2-8"
release: "Debian 3.0 (Woody)"
platforms: ["linux"]
url: "https://new.carta.tech/pvm_scatter"
---

# pvm\_scatter(3)

Sends to each member of a group a section of an array from a specified member of the group.

## NAME

pvm\_scatter - Sends to each member of a group a section of an array from a specified member of the group.

## SYNOPSIS

```
C    int info = pvm_scatter( void *result, void *data,
                  int count, int datatype, int msgtag,
                  char *group, int rootginst)
Fortran    call pvmfscatter(result, data, count, datatype,
                           msgtag, group, rootginst, info)
```

## PARAMETERS

- result

  **Pointer to the starting address of an array of length** *count* **of** *datatype* **which will be** **overwritten by the message from the specified root member of the group.**\

- data

  **On the root this is a** **pointer to the starting address of an array**  *datatype* **of local values** **which are to be distributed to the members of the group.** **If n is the number of members in the group, then this array of**  *datatype* **should be of length at least n\****count*. This argument is meaningful only on the root.\

- count

  Integer specifying the number of elements of  *datatype* to be sent to each member of the group from the root.\

- datatype

  Integer specifying the type of the entries in the result and data arrays. (See below for defined types.)

- msgtag

  Integer message tag supplied by the user. msgtag should be \>= 0.  It allows the user's program to  distinguish between different kinds of messages.\

- group

  Character string group name of an existing group.\

- rootginst

  Integer instance number of group member who performs  the scatter of its array to the members of the group.\

- info

  Integer status code returned by the routine. Values less than zero indicate an error.

## DESCRIPTION

*pvm\_scatter()* performs a scatter of data from the specified root member of the group to each of the members of the group, including itself. All group members must call pvm\_scatter(),  each receives a portion of the  *data* array from the root in  their local  *result* array. It is as if the root node sends to the ith member of the group *count* elements from its array *data* starting at offset i\**count* from the beginning of the *data* array. And, it is as if, each member of the group performs a corresponding receive of  *count* values of  *datatype* into its  *result* array. The root task is identified by its instance number in the group.

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.

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

## EXAMPLES

```
C:
   info =  pvm_scatter(&getmyrow, &matrix, 10, PVM_INT,
                      msgtag, "workers", rootginst);

Fortran:
   CALL PVMFSCATTER(GETMYCOLUMN, MATRIX, COUNT, INTEGER4,
  &                MTAG, 'workers', ROOT, INFO)
```

## ERRORS

These error conditions can be returned by  *pvm\_scatter*

- PvmNoInst

  Calling task is not in the group

- PvmBadParam

  The datatype specified is not appropriate

- PvmSysErr

  Pvm system error

## SEE ALSO

pvm\_bcast(3PVM), pvm\_barrier(3PVM), pvm\_psend(3PVM)