Hello all,

I have got the pseudo-code below that I would like to convert to c
language. 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

Let me just be a bit more specific:

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 language?
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.

Again, thank you all.

On 13 May, 15:20, Prime Mover hotmail.com> wrote:

Prime Mover wrote:

How can you determine it without knowing PI a priori?

Pietro Cerutti

On May 13, 3:55 pm, Spiros Bousbouras gmail.com> wrote:

I got 3.1415 using a billion points. Looks like it will converge very
slowly.

Also the granularity of the x,y points may affect the maximum accuracy
(because it introduces errors near the circular edge). Tried a sphere
too but not any better.

Pietro Cerutti said:

There's nothing in the above description that requires a knowledge of pi.

For example, you can draw a circle of radius r easily enough just by
applying the equation x^2 + y^2 = r^2 (no, that is not C code!) for all y
in the range -r to +r, taking the positive result and its negative
analogue for your x points. (Actually, it's even easier than that, because
there are other symmetries to exploit.)

Determining whether you're in the circle can be done either by tedious
inspection (a process not unlike floodfill) or (much faster) by
determining whether x^2 + y^2 <= r^2.

On 13 May, 16:02, Pietro Cerutti wrote:

Imagine a circle with radius is 1 and its center has coordinates
(0 , 0).
A random point with coordinates (x,y) will be inside the square
if -1 <= x <= 1 and -1 <= y <= 1
if ( x*x + y*y < 1) /* inside the circle */

On 13 May, 16:15, Bart freeuk.com> wrote:

And of course you must know that your random numbers
will be uniformly distributed within the square.

Pietro Cerutti wrote:

Write the expression for the area of a circle. Do the same for the
area of the superscribed square. Take the ratio of areas. It
contains PI.