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Commit c082338

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author
Thomas Weise
committed
Added Some Comments
1 parent dc2e28c commit c082338

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4 files changed

+29
-26
lines changed

4 files changed

+29
-26
lines changed

‎mpi/bareBones.c

Lines changed: 4 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -1,7 +1,7 @@
1-
#include <mpi.h>
1+
#include <mpi.h>// import MPI header
22

33
int main(int argc, char **argv) {
4-
MPI_Init(&argc, &argv);
5-
MPI_Finalize();
4+
MPI_Init(&argc, &argv);// initialize MPI
5+
MPI_Finalize();// shut down MPI
66
return 0;
7-
}
7+
}

‎mpi/basicInfo.c

Lines changed: 11 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -1,20 +1,23 @@
1-
#include <mpi.h>
2-
#include <stdio.h>
1+
#include <mpi.h>// import MPI header
2+
#include <stdio.h>// import for printf
33

44
int main(int argc, char **argv) {
55
int size, rank;
66

7-
MPI_Init(&argc, &argv);
7+
MPI_Init(&argc, &argv);// initialize MPI
88

9-
MPI_Comm_size(MPI_COMM_WORLD, &size);
10-
MPI_Comm_rank(MPI_COMM_WORLD, &rank);
9+
MPI_Comm_size(MPI_COMM_WORLD, &size);// get number of program instances
10+
MPI_Comm_rank(MPI_COMM_WORLD, &rank);// get own ID/address
1111

12-
if(rank == 0) {
12+
// often, an MPI application has a master and some slaves
13+
// master distributes tasks and combine partial results to final results
14+
// slaves receive partial task, compute partial result, and send to master
15+
if(rank == 0) { // the instance with rank=0 is often chosen as master
1316
printf("Hi from Master\n");
14-
} else {
17+
} else {// the others are often slaves
1518
printf("Just Slave %d out of %d\n", rank, size);
1619
}
1720

18-
MPI_Finalize();
21+
MPI_Finalize();// finalize = shut down MPI
1922
return 0;
2023
}

‎mpi/simplePointToPoint1.c

Lines changed: 11 additions & 11 deletions
Original file line numberDiff line numberDiff line change
@@ -1,28 +1,28 @@
1-
#include <mpi.h>
2-
#include <stdio.h>
1+
#include <mpi.h>// import MPI header
2+
#include <stdio.h>// needed for printf
33

44
int main(int argc, char **argv) {
55
int size, rank, s_msg, r_msg, next, prev;
66
MPI_Status status;
77

8-
MPI_Init(&argc, &argv);
9-
MPI_Comm_size(MPI_COMM_WORLD, &size);
10-
MPI_Comm_rank(MPI_COMM_WORLD, &rank);
8+
MPI_Init(&argc, &argv);// initialize MPI
9+
MPI_Comm_size(MPI_COMM_WORLD, &size);// get number of program instances
10+
MPI_Comm_rank(MPI_COMM_WORLD, &rank);// get own ID/address
1111

12-
next = ((rank + 1) % size);
13-
prev = ((rank + size - 1) % size);
14-
s_msg = ((size * rank) + next);
12+
next = ((rank + 1) % size);// next higher id, wrap from size-1 to 0
13+
prev = ((rank + size - 1) % size);// next lower id, wrap from 0 to size-1
14+
s_msg = ((size * rank) + next);// the example message, just some number
1515

16-
if((rank % 2) == 0) {
16+
if((rank % 2) == 0) {// even rank: message to next, receive from prev
1717
MPI_Send(&s_msg, 1, MPI_INT, next, 42, MPI_COMM_WORLD);
1818
MPI_Recv(&r_msg, 1, MPI_INT, prev, 42, MPI_COMM_WORLD, &status);
19-
} else {
19+
} else {// otherwise: receive from rev, send to next
2020
MPI_Recv(&r_msg, 1, MPI_INT, prev, 42, MPI_COMM_WORLD, &status);
2121
MPI_Send(&s_msg, 1, MPI_INT, next, 42, MPI_COMM_WORLD);
2222
}
2323

2424
printf("id: %d, next: %d, prev: %d, send: %d, recv: %d\n", rank, next, prev, s_msg, r_msg);
2525

26-
MPI_Finalize();
26+
MPI_Finalize();// shut down MPI
2727
return 0;
2828
}

‎mpi/simplePointToPoint2.c

Lines changed: 3 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -1,6 +1,6 @@
1-
#include <mpi.h>
2-
#include <stdio.h>
3-
#include <string.h>
1+
#include <mpi.h>// import MPI header
2+
#include <stdio.h>// needed for printf
3+
#include <string.h>// needed for strlen
44

55
int main(int argc, char *argv[]) {
66
char message[20];

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