## SIMULATION DIGEST VOL. 2, NUM. 2

### SIMULATION DIGEST VOL. 2, NUM. 2

Volume: 2, Issue: 2, Thu May  5 13:18:41 EDT 1988

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| TODAY'S TOPICS |
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(1) Simulation with Combinatoric Problems
(2) Economic Modeling
(3) IMACS World Congress

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Path: pur-ee!gapp

Newsgroups: comp.simulation
Subject: simulation of Combinatorics problem
Date: 2 May 88 21:35:13 GMT

Distribution: usa
Organization: Purdue University Engineering Computer Network

Hi, dear netters:

I have a problem in simulation and need some help from the netters. Here
is what it looks like.

Suppose I have a mesh grid of colored squares, say there are N=nxn of
them. Suppose I also know that K of them are BLUE and N-K of them are RED.
Let the coordination of these squares be denoted by (x,y) where 1 <= x <= n
and 1 <= y <= n. We define the distance of two squares (i1, j2) and (i2, j2)
by d=abs(i1-i2) + abs(j1-j2), i.e., the Manhattan distance between them.
Given a pattern of how these K BLUEs are scattered among the RED squares, the
distance of this pattern would be the maximal distance between two BLUE
squares.

What I'd like to find is the expected distance of the patterns
with the uniform distribution P(K, N), which means there are K BLUEs in
the N (nxn) square grids. The most intuitive way for me is to write a
program that generate a pattern first, counts the distance of two farest
squares, sums there distances together, and average it by dividing with
the number of possible distribution patterns.

What hit me bad here is the number of patterns would be C(N,K)
which is a combinatoric value. It is just infeasible to write a program
actually that generate all there patterns, counts the max distance of
that pattern, and then find the expected distance as the result. If I
do it this way, all computer users here would kill me for sure.

Is there any good ( or tricky ) statistical way that allows me
to run this simulation instead? I asked a couple of friends here, but
this sort of combinatorics problem just keep them far away from me.

Thanks a lot in advance for the help.

pur-ee\!ed\!aynang

PS. Please mail to my e-mail address if possible. I am using a lab account
to post this news.

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Path: uw-june!jon

Newsgroups: comp.simulation
Subject: Economic modelling
Keywords: simulation, modelling, economics, world bank
Date: 3 May 88 15:52:38 GMT
Organization: U of Washington, Computer Science, Seattle

The April 1, 1988 issue of DATAMATION includes an article, "Economic
Modeling Gains Despite Accuracy Concerns," by Gary McWilliams (pps. 43-54).
I am not familiar with this field, and the article never really explains
what the inputs and outputs of the models are, where they come from or
how they are validated.  Nevertheless, people apparently use them to
forecast economic trends and seem to regard them as useful.  One model,
called Project Link, includes more than 20,000 equations.

Much of the article appears to be based on an interview with Sam Cole,
economist and model builder at SUNY Buffalo, and author of GLOBAL MODELS
AND THE INTERNATIONAL ECONOMIC ORDER (Oxford Pergamon, 1977).  The article
reports,

"The World Bank uses a global model in its lending, says Cole, sometimes to
the detriment of its debtors.  'When the World Bank lends [a country] money,
it expects that country to have a [repayment] plan, and usually pursuades the
country to accept World Bank forecasts.  Since its forecasts are usually
wrong, these countries end up with debts and no way to repay them,' says
Cole.  The World Bank's use of optimistic growth forecasts often are built
into the models for political reasons, according to Cole."

- Jon Jacky, University of Washington

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Date: Tue, 3 May 88 17:09:35 EDT

Subject: IMACS World Congress

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=========================
* 12th IMACS WORLD CONGRESS *
* ON SCIENTIFIC COMPUTATION *
=========================
July 18-22, 1988 - Paris, France
================================

The 12th. IMACS World Congress will take place at the historic site of
the Sorbonne/Lycee  Louis le Grand  in the Quartier  Latin,  a central
area of Paris known since the Middle  Ages for its prestigious Schools
and  its  University.   The program of  the Congress features some 900
papers, to be  presented by authors  from almost every  country in the
world.   The topics  cover   a wide  range of  interests,    including
Computational Mathematics,  Numerical  Analysis, Modelling of Systems,
AI and Expert systems, Computational Physics, Computational Acoustics,
Applications in Science and Engineering, and Hardware and Software for
Scientific Computation.

Registration  forms, and  the preliminary  program,  which contains  a
listing of all  papers  and social events,  may be obtained by writing
to:

IMACS Secretariat
Attn:  K. Hahn
Rutgers University
Dept. of Computer Science
New Brunswick, NJ  08903  USA

Tel:  201-932-3998

or to :

IMACS Congress Secretariat
I.D.N.  BP 48
F 59651 Villeneuve d' Ascq . Cedex
France
Phone (33) 20 91 01 15

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| END OF SIMULATION DIGEST |
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