calculating PI with a parallel algorithm

[Prime Mover]

Hello all,

I have got the pseudo-code below that I would like to convert to c
language (or maybe java). The algorithm calculates Pi value. I am
somewhat
familiar with C language, but I am just starting to learn parallel
programming.
In this specific example, the idea seems to be simple: one must
subdivide the main loop into pieces that can be executed by
independent "tasks" (computers??).

Then, each "worker task" executes a part of the loop a certain
number
of times, independently of the other worker tasks. One specific task
plays the role of "master task", which will collect and sum the
results of the worker tasks:

% descriptive algorithm:
1. Inscribe a circle inside a square
2. Generate random points inside the square
3. Determine the number of points that fell inside the circle
4. Let r be the number of points inside the circle divided by the
total number of points
5. Pi is approximately equal to 4*r
6. The more points are generated, the more is the precision in P
value


% pseudo-code (parallel):
1. npoints = 10000
2. circle_count = 0
3. p = number of tasks
4. num = npoints/p
5. find out if I am MASTER or WORKER
6. do j = 1,num
7. generate 2 random numbers between 0 and 1
8. xcoordinate = random1
9. ycoordinate = random2
10. if (xcoordinate, ycoordinate) inside circle then
circle_count = circle_count + 1
11. end do
12. if I am MASTER
13. receive from WORKERS their circle_counts
14. compute PI (use MASTER and WORKER calculations)
15. else if I am WORKER
16. send to MASTER circle_count
17. endif

My (understading) problem starts in the line 5 of the pseudo-code:
"5. find out if I am MASTER or WORKER"
How would I specificy a "worker"? Would that be another computer?
If yes, how can I access this remote computer in the calculations, in
C or JAVA?
If yes, it means that I have to have a LAN or something to perform
tests?
I have found that there are some libraries such as OMP or MPI that
could be used, but I'd like to know if there is a more "raw" way of
doing this first.

Any help would be much appreciated.

I thank you all in advance.

(I was advised for someone in comp.lang.c to post this question here
or some similar group, instead of in comp.lang.c).

[Greg Lindahl]

Post by Prime Mover
I have got the pseudo-code below that I would like to convert to c
language (or maybe java).

The problem and algorithm you describe are available with most MPI
implementations as an example program. Try googling "mpi pi".

Post by Prime Mover
(I was advised for someone in comp.lang.c to post this question here
or some similar group, instead of in comp.lang.c).

Rude, aren't they?

-- greg

[j***@hotmail.com]

Post by Prime Mover
Hello all,
I have got the pseudo-code below that I would like to convert to c
language (or maybe java). The algorithm calculates Pi value. I am
somewhat
familiar with C language, but I am just starting to learn parallel
programming.
In this specific example, the idea seems to be simple: one must
subdivide the main loop into pieces that can be executed by
independent "tasks" (computers??).
Then, each "worker task" executes a part of the loop a certain
number
of times, independently of the other worker tasks. One specific task
plays the role of "master task", which will collect and sum the
1. Inscribe a circle inside a square
2. Generate random points inside the square
3. Determine the number of points that fell inside the circle
4. Let r be the number of points inside the circle divided by the
total number of points
5. Pi is approximately equal to 4*r
6. The more points are generated, the more is the precision in P
value
1. npoints = 10000
2. circle_count = 0
3. p = number of tasks
4. num = npoints/p
5. find out if I am MASTER or WORKER
6. do j = 1,num
7. generate 2 random numbers between 0 and 1
8. xcoordinate = random1
9. ycoordinate = random2
10. if (xcoordinate, ycoordinate) inside circle then
circle_count = circle_count + 1
11. end do
12. if I am MASTER
13. receive from WORKERS their circle_counts
14. compute PI (use MASTER and WORKER calculations)
15. else if I am WORKER
16. send to MASTER circle_count
17. endif
"5. find out if I am MASTER or WORKER"
How would I specificy a "worker"? Would that be another computer?
If yes, how can I access this remote computer in the calculations, in
C or JAVA?
If yes, it means that I have to have a LAN or something to perform
tests?
I have found that there are some libraries such as OMP or MPI that
could be used, but I'd like to know if there is a more "raw" way of
doing this first.
Any help would be much appreciated.
I thank you all in advance.
(I was advised for someone in comp.lang.c to post this question here
or some similar group, instead of in comp.lang.c).

This problem is explained and solved in Section 3.8 of the book
_Using MPI. Portable parallel programming with the message-passing
interface_ 2nd edition, by Gropp, Lustk, and Skjellum.

HTH

Jomar

[gudny]

Here is the code to the third chapter of the book:
http://www-unix.mcs.anl.gov/mpi/usingmpi/examples/intermediate/main.htm
one of the example programs is the pi problem.
Gudny

[gudny]

Here is the code to the third chapter of the book:http://www-unix.mcs.anl.gov/mpi/usingmpi/examples/intermediate/main.htm
one of the example programs is the pi problem.
Gudny

oh, sorry, exchange "intermediate" for "simplempi" in the link!