Re: Evenly distributed source

There are useful articles available at mathworld.wolfram.com explaining uniform sampling of points from spheres, disks circles and a few other entities.

http://mathworld.wolfram.com/CirclePointPicking.html
http://mathworld.wolfram.com/SpherePointPicking.html
http://mathworld.wolfram.com/DiskPointPicking.html

The disk point picking transformation that is given will result in the same distribution that Alberto provided without requiring that (1-pi)/pi of the random points be discarded.

Jeff Wilkinson

Jeff Wilkinson
Medtronic Technical Fellow, Sr Principal R&D Engineer
Medtronic, Inc -- 8200 Coral Sea St NE -- Mounds View, MN 55112 USA
763-526-0483

Hi Sebastien,

Be careful, MYRHO begins with an M, it will be interpreted as
an integer. Call it RHOMY.

But I don't think that it is correct to sample a radius between 0 and RADIUS,
as you do. There are many more points at large radii than at small ones,
and your sampling fails to account for this.
You should sample the points in a square of edge 2.D0*RADIUS, and reject if
a point falls outside the circle:
  123 CONTINUE
       XXX = -RADIUS + FLRNDM(XDUMMY) * (TWOTWO*RADIUS)
       YYY = -RADIUS + FLRNDM(YDUMMY) * (TWOTWO*RADIUS)
       IF((XXX**2+YYY**2) .GT. RADIUS**2) GO TO 123
       ................................................
       XFLK (NPFLKA) = XXX
       YFLK (NPFLKA) = YYY

Alberto

On Fri, 30 Jan 2009, Sebastien WURTH wrote:

> Hello,

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Received on Tue Feb 03 2009 - 21:16:44 CET