simulation@uflorida.cis.ufl.edu (Moderator: Paul Fishwick) (05/09/91)
Volume: 21, Issue: 8, Wed May 8 16:45:46 EDT 1991 +----------------+ | TODAY'S TOPICS | +----------------+ (1) RE: Pendulum Problem (2) WANTED: Network Modelling Software (3) Network Analysis (4) Qualitative and Qualitative Interfaces (5) BOOK: The Art of Computer Systems Performance Analysis (6) WANTED: Tools for Modeling Surface Phenomena * Moderator: Paul Fishwick, Univ. of Florida * Send topical mail to: simulation@bikini.cis.ufl.edu OR post to comp.simulation via USENET * Archives available via FTP to bikini.cis.ufl.edu (128.227.224.1). Login as 'ftp', use your last name as the password, change directory to pub/simdigest. Do 'type binary' before any file xfers. * Simulation Tools available by doing above and changing the directory to pub/simdigest/tools. ----------------------------------------------------------------------------- Date: Fri, 26 Apr 91 09:45:48 -0400 From: "Paul Fishwick" <fishwick@fish.cis.ufl.edu> To: simulation@ufl.edu Subject: Pendulum Problem >From uflorida!caen!sdd.hp.com!cs.utexas.edu!ut-emx!emx.utexas.edu Fri Apr 26 09:45:19 EDT 1991 Article: 556 of comp.theory.dynamic-sys Path: uflorida!caen!sdd.hp.com!cs.utexas.edu!ut-emx!emx.utexas.edu From: hasan@emx.utexas.edu (David A. Hasan) Newsgroups: comp.theory.dynamic-sys Subject: double pendulum Date: 25 Apr 91 19:56:23 GMT Sender: hasan@ut-emx.uucp Organization: UTexas Center for Space Research I have failed from within my newsreader and my mailer in trying to send mail directly to richard. So here is my response to his questions about potential energy of the double pendulum problem. Sorry to the rest of you for its length... In article <puchm.672390379@cutmcvax> you write: > > > T1 = 1/2 * m1 * l1 * th1. > T2 = 1/2 * m2 * (l1 * th1. + l2 * th2.) > I think that you meant to *square* the velocity terms in these expressions, right? > U1 = -m1 * g * l1 * cos(th1) > U2 = -m2 * g * l2 * cos(th2) * l1 * cos(th1) > > Are the potentials correct ? Except for the typo in U2 (the two l-cosine terms should be added together instead of multiplied), this looks ok. > If YES, why ? > If NO, why and what are the correct ones? > The above questions should indicate a total lack of > understanding as to the formulation of the potentials. > "Potential energy" as a fundamental principal on which to base your analysis has some difficulties if the form of the potential is not obvious to start with. In fact, potential energy is another way of representing the "work" done by so-called conservative forces. In a uniform gravity field (situations where the effect of gravity is usefully modeled as a constant acceleration due to gravity -- g), the potential has the form U = mgh where h is the distance *above* some arbitrarily selected reference. ("above" = "opposed to gravity") The reasons why the reference can be selected arbitrarily are not really important (it is because the FORCE due to gravity is calculated by differentiating the potential, and in the process of differentiating all constants drop out), but is is *crucial* that you select ONE reference (sometimes called a "datum") and use it for all your derivations. Based on the expressions you have given, the reference seems to be the "root" hinge of the system. The form U=mgh is derived from basic princples as follows: The potential energy is defined as the negative of the work done by gravity on the mass in moving it from the datum to its location. Work done is a dot-product of the gravity force and the displacement. But the gravity force is downward and the displacement is upward, so the dotproduct in the definition of work gives you work done by gravity = (force vector) . (displ. vector) = - (mg) (h) = -mgh But the potential energy is the NEGATIVE of this: U = -( work done by gravity ) = -( - mgh ) = mgh In your case, the masses are BELOW the reference, so h (which is defined as the height ABOVE the reference) is a negative quantity. Of course, it is useful in this problem to work with (positive) distance quantities such as l_1 * cos(theta_1) l_1 * cos(theta_1) + l_2 * cos(theta_2) which are distances of the masses BELOW the reference. This is where the negative sign comes in. Now, the question you ask about "how to derive the potential energy" is actually more involved than this in general. I don't know exactly what directions your work will take you, but if your simulations are going to handle more complex systems, you might be required to go beyond the discussion above. Ultimately, it all boils down to understanding what forces are acting on the system and representing as many of them as possible by a potential energy. (By the way, this is not always possible, for example if the pendulum is suspended in a fluid, you'll have to deal with the fluid forces using work principles directly.) In my work, I'm dealing with flexible vehicles in orbit. The flexibility intoduces internal stresses which do work and can be modelled by a potential energy. And the gravitational forces can also be modelled as a potential energy. However, these potential energies have a different form than the (simple) U=mgh discussed above. The differences are due primarily to the fact that the forces themselves act in a significantly more complicated manner than the force due to gravity in a uniform gravity field. If all you need to do in model point masses and rigid bodies near the surface of the earth, then the U=mgh stuff will get you quite far. Just be warned, however, that the fundamental principles are somewhate "hidden" by the notion of potential energy. Finally, beware that there are some people out there who discuss "potential functions". The field of celestial mechanics is full of these. It is an unfortunate and often confusing fact that potential functions and energies differ in their definitions by a minus sign. So if you go beyond U=mgh in your efforts, pay attention to the small print. -- | David A. Hasan | hasan@emx.utexas.edu ------------------------------ Date: Tue, 30 Apr 91 15:35:10 EDT From: rgirard@ncs.dnd.ca (R. Girard) To: fishwick@bikini.cis.ufl.edu Subject: LOOKING FOR NETWORK MODELLING SOFTWARE I am looking for a network simulator or simply a set of C routines I could use to build to a rough model of a packet switching network toward optimization of performance and reliability? I was told that there is at least one such modelling tool in the public domain. It is called XSIM and is supposed to model a tcp/ip network. I have left posted Thanks! <address this by e-mail to fishwick@uflorida.cis.ufl.edu> ------------------------------ Return-Path: <samuels@starbase.mitre.org> Date: Wed, 1 May 91 07:55:19 EDT From: samuels@starbase.MITRE.ORG (Mike Samuels) To: simulation@bikini.cis.ufl.edu Subject: Network Analysis help request I'm working on a scenario generator for an automated highway simulation. My marching orders are to provide a list of vehicles with start times, origin and destination, and the optimal path to get from origin to destination. The path should be optimized for shortest delay within the capacity constraints of the network. The shortest delay is straightforward. Floyd developed an algorithm awhile back that solves the shortest path problem from any source and any sink; i.e., a node can be both a source and sink at the same time. The literature calls this the "multiterminal shortest chain problem". The problem is when you add capacity constraints, the problem seems to get a lot more complex. The out-of-kilter algorithm solves the problem if you have 1 source and 1 sink, or perhaps a set of sources and a separate set of sinks, but it doesn't extend Floyd's multiterminal chain solution to include capacities. The only algorithm we've run across that comes close is from Kleinrock, Volume 2, p. 340 ff.; he calls it the "Flow Assignment" algorithm. It is a gradient analysis solution, supposedly inching its way towards a solution without getting too close to the capacity - at that point, it will blow up. The algorithm uses Floyd as part of its solution, so it looks promising. However, Kleinrock's description is a little terse - nothing like the depth provided in a network analysis book (e.g., "Fundamentals of Network Analysis" by Phillips & Diaz-Garcia). I've printed out each step of the algorithm, and the results look terrible. Does anyone know of a better algorithm? All the network analysis literature I've seen discusses numerous variations on the shortest path algorithm, an equivalent number on maximal flow, and then a few variations of the out-of-kilter generalized solution. Noone seems to cover an extension of the Floyd algorithm to include capacity constraints. Thanks for any help you can provide. Michael Samuels The MITRE Corporation samuels@mitre.org Mailstop W448 (703) 883-7828 7525 Colshire Drive FAX: (703) 883-6435 McLean, VA 22102 ------------------------------ Date: Thu, 2 May 1991 18:07:26 +0200 X400-Originator: guasch@esaii.upc.es X400-Mts-Identifier: [/PRMD=iris/ADMD= /C=es/;910502180726] X400-Content-Type: P2-1984 (2) Content-Identifier: 42 Conversion: Prohibited From: Antoni Guasch <guasch@esaii.upc.es> To: simulation@ufl.edu (Receipt Notification Requested) (Non Receipt Notification Requested) Subject: Quantitative & Qualit. interfaces We are the Simulation Group of the Computing and Control Engineering Department at the Politechnical University of Catalonia, Barcelona (Spain). We are currently starting a research project in Qualitative Simulation in general and the interface between quantitative and qualitative modeling in particular. We are very interested on any work (papers, ongoing project, research groups) related to the interface between both modeling methodologies. We will forward the received information to the list. Alvaro de Albornoz Departament ESAII Universitat Politecnica de Catalunya Diagonal 647 - 2 planta 08028 Barcelona e-mail: ALBORNOZ@ESAII.UPC.ES ------------------------------ To: comp-simulation@Decwrl.dec.com Path: nntpd.lkg.dec.com!manage.enet.dec.com!jain From: jain@manage.enet.dec.com (Raj Jain, DEC, 550 King st, Littleton, MA, 01460, 508-486-7642, Fax:486-5279) Newsgroups: comp.simulation Subject: New Book Announcement: The Art of Computer Systems Performance Analysis Date: 5 May 91 14:19:34 GMT Sender: newsdaemon@shlump.nac.dec.com Organization: Digital Equipment Corporation The Art of Computer Systems Performance Analysis: Techniques for Experimental Design, Measurement, Simulation, and Modeling By Raj Jain John Wiley & Sons, New York, ISBN 0471-50336-3, 720 pages, April 1991. This book emphasizes simple-to-use techniques that can be applied by computer system designers, managers, marketing professionals, buyers, analysts, and others who need to compare alternative systems (computers, processors, devices, networks, databases, operating systems, languages, algorithms, or applications) or manage such projects. The 720-page volume covers virtually every aspect of systems evaluation from performance specification, capacity planning, and monitoring systems in use, to summarizing measured data, designing experiments, simulating future designs, and modeling the effect of proposed changes. The book reveals how to avoid common mistakes, and shows how to protect oneself from misleading analyses presented by others. Given a set of performance data on two or more systems, it is sometimes possible to manipulate the data, benchmarks, analysis, metrics, or data presentation such that either system can be shown to outperform the other! More than 150 examples and case studies cover topics such as evaluation of microprocessors, RISC processors, remote procedure calls, the UNIX operating system, garbage collection algorithms, interconnection networks, local area networks, text-formatting programs, cache and scheduler design issues and more. It has been selected as the *main* selection by the NewBridge Library of Computer and Information Sciences (LCIS) bookclub. EXPERTS' OPINIONS... "At last, a welcome and needed text for computer professionals who require practical, ready-to-apply techniques for performance analysis. Highly recommended!" --- Professor Leonard Kleinrock, Univ of California at Los Angeles "The Art of Computer Systems Performance Analysis is an extraordinary book. It has a practical, problem-oriented style which appeals immediately to engineers engaged in real-world design and analysis." --- Vint Cerf, Chairman, ACM SIGCOMM "An entirely refreshing text which has just the right mixture of theory and real world practice. The book is ideal for both classroom instruction and self study." --- Professor Raymond L. Pickholtz, President, IEEE Communications Society "An extraordinarily comprehensive treatment of both theoretical and practical issues." --- Dr. Jeffrey P. Buzen, Internationally known performance expert "It is the most thorough book available to date." --- Professor Erol Gelenbe, Universite Rene Descartes, Paris "This is an unusual object, a textbook that one wants to sit down and peruse. The prose is clear and fluent, but more important, it is witty." --- Allison Mankin, in Simulation "The frequent use of case studies was effective and sometimes entertaining." --- Craig Partridge, Editor, Computer Communication Review "It is extremely comprehensive -- I am hard pressed to think of a performance evaluation technique that isn't discussed here. The emphasis is on practical techniques that could be used without a great deal of mathematical sophistication." ---Professor David Finkel, Performance Evaluation Review "I found that the pace of the material was very even, which makes it a particularly suitable text from which to teach." --- Professor Jon Crowcroft, Univ College London, in Computer Communications A LIST OF INTERESTING "DON'T MISS" TOPICS o How to show a better performance for your system without any changes (Beware of ratio games played by your competitors) (Performance games people play) [p 130-131, 146, 165-174] o Four rat holes to avoid in performance presentations (Four easy ways to stall anybody's performance presentation) [p 162] o Twenty six ways to stall your competitor's presentation (How to kill your competitors' performance presentations) [p 161-162] o Six mistakes to avoid in preparing charts for presentations [p 144-146] o Six tricks to watch out for in your competitors' presentation graphics [p 146-150] o Twenty two mistakes to avoid in your performance analyses [p 14-22] o Ten problems in computer systems capacity planning [p 125-127] o Twelve common mistakes in benchmarking computer systems [p 127-130] o Seven benchmarking games to watchout [p 130-131] o Thirty four ways to improve your programs' performance [p 114-116] o Twenty six guidelines for good graphics in your presentations [p 141-143] o Eleven mistakes to avoid in empirical modeling [p 266-269] o Six common mistakes in experimental design [p 278-279] o Eight mistakes that may lead to incorrect simulation results [p 394-395] o Seven reasons why most simulations fail [p 395-397] o Six guidelines for selecting seeds for random number generators [p 453-455] o Six myths about random-number generators [p 455-458] o Thirteen system behaviors that are difficult to analyze using queueing models [p 620-622] OTHER TOPICS DISCUSSED I AN OVERVIEW OF PERFORMANCE EVALUATION o When to measure, simulate, or model? o How to select the right performance criteria? o How to specify performance requirements? II MEASUREMENT TECHNIQUES AND TOOLS o Which benchmarks are commonly used in the industry? o How to design the right workload for your system? o How to monitor your distributed systems? o How to use accounting logs to determine the workload of your system? o How to plan and manage capacity required for your computer installation? III PROBABILITY THEORY AND STATISTICS o How to summarize measurements with a single number? o How to report variability? o How much confidence can you put on data with a large variability? o How many measurements do you need to compare two systems? o How to compare systems using multiple benchmarks? IV EXPERIMENTAL DESIGN AND ANALYSIS o How many experiments do you really need? o How to get the most information with the minimum number of experiments? o Is one system really better than another? Or is it the effect of very different benchmarks? o How to isolate measurement errors? o How to check if a model is adequate? Part V: SIMULATION o What language should you use for a simulation? o How to verify and validate a simulation model? o How long to run a simulation? o How to generate random numbers and how to select seeds? o What probability distributions should you use? Part VI: QUEUEING MODELS o How to use simple queueing models to quickly answer common questions? o How to obtain response time, queue lengths, and device utilizations? o How to obtain bounds, variance, and other statistics on system performance? o How to subdivide a large queueing network model and solve it? FOR INSTRUCTORS AND STUDENTS Designed to be the main textbook for a first course on performance evaluation, it provides a comprehensive treatment of all aspects of performance analysis. You no longer need separate books for measurement, statistics, experimental design, simulation, and queueing theory. If you teach a course on computer systems such as architecture, engineering, networks, or databases, you can use it as a supporting textbook to cover performance issues. The chapters are organized so that each one can be presented in 45 minutes, with time left over to discuss the exercises and solutions in a typical 55-minute class. This makes the text ideally suited for a one- or two-semester course. Practice exercises at the end of each chapter can be used for homework. Solutions to the exercises appear at the end of the book. TABLE OF CONTENTS The book consists of 36 chapters divided into six parts. The chapter titles are listed below. 1. AN OVERVIEW OF PERFORMANCE EVALUATION: Introduction. Common Mistakes and How to Avoid Them. Selection of Techniques and Metrics. 2. MEASUREMENT TECHNIQUES AND TOOLS: Types of Workloads. The Art of Workload Selection. Workload Characterization Techniques. Monitors. Program Execution Monitors and Accounting Logs. Capacity Planning and Benchmarking. The Art of Data Presentation. Ratio Games. 3. PROBABILITY THEORY AND STATISTICS: Summarizing Measured Data. Comparing Systems Using Sample Data. Simple Linear Regression Models. Other Regression Models. 4. EXPERIMENTAL DESIGN AND ANALYSIS: Introduction to Experimental Design. 2**k Factorial Designs. (2**k)r Factorial Designs with Replications. 2**(k-p) Fractional Factorial Designs. One-Factor Experiments. Two-Factor Full Factorial Design without Replications. Two-Factor Full Factorial Design with Replications. General Full Factorial Designs with k Factors. 5. SIMULATION: Introduction to Simulation. Analysis of Simulation Results. Random-Number Generation. Testing Random-Number Generators. Random-Variate Generation. Commonly Used Distributions. 6. QUEUEING MODELS: Introduction to Queueing Theory. Analysis of a Single Queue. Queueing Networks. Operational Laws. Mean-Value Analysis and Related Techniques. Convolution Algorithm. Hierarchical Decomposition of Large Queueing Networks. ABOUT THE AUTHOR With over sixteen years of experience in the field of computer systems performance, Raj Jain is a Senior Consulting Engineer at Digital Equipment Corporation. He received the Ph.D. degree in Computer Science from Harvard University and has taught courses on performance analysis at Massachusetts Institute of Technology. Author's Address: Raj Jain, 137 Dutton Road, Sudbury, MA 01776-2804, USA. Internet: Jain@Erlang.enet.DEC.Com BOOK REVIEWS o Simulation, Vol. 56, No. 1, January 1991, p. 60. o Computer Communications Review, Vol. 21, No. 1, January 1991, p. 13. o Performance Evaluation Review, Vol. 18, No. 3, November 1990, p. 21-22. o ConneXions, Vol. 5, No. 2, February 1991, p. 22. o Computer Communications, Vol. 14, No. 4, May 1991. o Computer Marketing Newsletter, Vol. XIV, No. 12, May 1991, p. 4. The book (ISBN 0471-50336-3, LCCN: QA76.9E94J32 1991, 720 pp., April 1991, $52.95, Hardcover) is published by John Wiley & Sons, 1 Wiley Drive, Somerset, NJ 08875, Phone: (908)-469-4400, (800)-225-5945 Ext 2499, Fax: (908)-302-2300. It is available NOW at most technical bookstores in the United States. It can also be obtained directly from the publisher. ------------------------------ Date: Sun, 5 May 1991 14:57 +8:00 From: THUDSONDL@cc.curtin.edu.au Subject: request for software help To: simulation@bikini.cis.ufl.edu X-Envelope-To: simulation@uflorida.cis.ufl.edu X-Vms-To: IN%"simulation@uflorida.cis.ufl.edu" To whom it may concern: I am interested in tools that will help in the construction of models of dynamic surface phenomena such as forest fires, oil spills, epidemic spreads, etc. Could anyone there direct suggest some software that has been designed for this purpose - perhaps some relevant literature as well. Doug Hudson School of Computing Science Curtin University of Technology Perth Western Australia ------------------------------ END OF SIMULATION DIGEST ************************