Ventana software support forum

J.J. Laubles is extremely clear (and concise!) in providing the principle that must guide much (but maybe not all?) statistical testing: If you can prove A implies B with only a 5% chance of error. And, if you can prove that B is not true, then youve proved that A is not true with only a 5% chance o...

Alan, I was right with you, buddy, up until you said that FIMLOF is mathematically rigorous from practical assumptions to practical conclusions. I take it the "practical assumptions" are not the same as the unrealistic "first assumptions" used in the mathematical derivation? So w...

I greatly appreciate John Stermans comments concerning the question whether statistical estimates have any rational claim on our attention other than widespread use and anecdotal evidence of usefulness. John gives many areas where statistical estimates are being used. So, chalk one up for widespread...

Jack Ring writes: " ...But I am disturbed by the theme that one should model what people do and how they make decisions. I thought the purpose of modeling was to discern the key demands and resources so that the allocation process itself is improved (including manager behaviors)." I dont t...

George Richardson offers a further refinement to his elegant resource allocation formulation. There is, though, still a problem, isnt there? The new formulation does not ensure that the resource will be as fully allocated as possible. If Tj maxes out, so that Tj takes less resource than it could hav...

Steve, Georges solution is very fast to model. The formulation has the nice property that all of the resource will be allocated. Lots of people use this allocation scheme. Unfortunately, the formulation only works well when the resource is in very short supply. Otherwise, the formulation may result ...

The **intent** of the fatigue molecule is to do what Kevin describes. The table function shows the maximum effect of working, any given amount of time - say 60 hours per week. After working a single day at that rate one would not feel very fatigued, of course. But, after working, say, three months o...

Further to Jim Thompsons comments about how to find out how folks really make decisions. I recently was involved in a situation where folks just couldnt put their finger on how they allocated people between the different stages of their product development process. (Note: These were the folks who ac...

Geoff, Your formulations are very nice. But, isnt it **usually** true that non-negativity formulations involving "dt" are "short cuts"? In our aggregated models, isnt a table function usually part of conceptually better solution? A common example would be where an "effect of...

Marion, you suggest that an "SD [flow] has to be divided into inflow .. and outflow...". But SD lets you have negative in- or out-flows, right? A bigger problem involves units. Consider your second example: > In another case: (1-population/capacity)*population > a derivation into in-flow a...

Id like to announce our new web site describing MITs new distance program in system dynamics http://caes.mit.edu/Programs/dist_sys_cert.html. In brief, MIT is offering a four-course sequence offered at a distance via steaming video, the web, and (if you wish) video tape. Any or all courses may be ta...

Aitor, Please correct me if Im wrong, but I think that... There is a difference in practice in that System Dynamics Models are almost always centrally interested in feedback processes. In contrast discrete event models are almost always centrally concerned with impact of stochastic processes on thin...

Just a little point on instantaneous feedback. I think there is a (single?)
class of examples in which simultaneity exists in the real world. If you
push down on a table, doesnt the table instantaneously push up against you?

Regards,
Jim Hines
MIT and LeapTec
Jim Hines JHines@mit.edu

Guenter,

As far as I know the only general and fairly reliable way to analyze a
causal loop diagram is to build a simulation model of it and then analyze
the simulation.

Regards,
Jim Hines
MIT and LeapTec
From: "Jim Hines" <JimHines@Interserv.com>

Good pricing formulations that Ive seen do not explicitly depend on "demand" and "supply", because (in most markets) no one knows these quantities. Instead, good pricing formulations often work from "inventory" - if inventories are high, prices are reduced; if inventori...