Subject: Please comment

From: Geoffrey Fox <[email-masked]>
Date: Fri, 24 Mar 2000 15:02:04 -0500

Geoffrey Fox  [email-masked] [email-masked]
Phones Cell 315-254-6387  Syracuse Office 315-443-2163 FSU Office 850-644-4587

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Date:    Thu, 23 Mar 2000 20:29:05 -0500
From:    Quant Marjorie V 2dLt AFRL/IFSB <[email-masked]>
To:      "[email-masked]'" <[email-masked]>,
	 "[email-masked]'"
	 <[email-masked]>
Subject: FW: Assign 4 Question

Hello, 

I need some clarification on assignment 4.  As I understand the problem, we
are to sum a "function" between two particles of a system.  There are a
total of N values for the particles in the system, so we must calculate the
sum for each x[N] and y[N] (are we not doing this calculation twice, once
from the x side and then once again from the y side?).  I have several
questions:

*(UNDER THE SECTION ENTITLED "CORRELATION PROBLEM") The problem seems to
contradict itself by first saying that you should take the summation over j,
from 0 to N of f(x[i],y[j]); where only the j component (and thus y) is
changing for one x...the x[i] is the outer loop.  Later in the assignment,
the instructions explain that this is the "very bad message passing
algorithm" ..you should instead set y[j] as the outer loop.

*I am unsure as to what the function we are summing over should be; is it
f(a,b) = [a^2+b^2]?  If so, is x[i] an array to hold all values for a^2 and
y[j] an array to hold all values of b^2?  Should the function read
f(a[i],b[j]) = (a[i]^2+b[j]^2)?

*Are both x[i] and y[j] separated onto n processors?  Then x[i] is
calculated while y[j] is passed in a ring through all the processors until
the original y[j] values return to the original processor, then the next
x[i+1] value is computed?

*What exactly are we computing with (a^2+b^2)?  Should this be a distance
(such as the sqrt of (a^2+b^2))?

Thank you.

Marjorie Quant

_________________________________
Marjorie V Quant, Lt, USAF
AFRL/IFSB
525 Brooks Road
Rome NY, 13441

EMail:  [email-masked]
DSN:  587-4679  Comm:  (315) 330-4679 

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