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

Please insert the following in your Digest / Thanks in anticipation

***************************************************************************

=========================

* 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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