Publications

OP-EDS

  1. Garrow, L. (2023, March 3). What can we do to make sure the FAA and Southwest Airlines fiascos never happen again? Invited op-ed piece for Scientific American.
  2. Garrow, L.A. (2022, January 21). America’s airlines face a long road back to normal. Invited op-ed piece for Barron’s.
  3. Garrow, L.A. (2021, November 4). Airlines are still reeling from the pandemic. Brace for a bumpy holiday travel season. Invited op-ed piece for Barron’s.

BOOK

  1. Garrow, L.A. (2010). Discrete Choice Modelling and Air Travel Demand: Theory and Applications. Ashgate Publishing: Aldershot, United Kingdom. pp. 286.

BOOK CHAPTERS

  1. Garrow, L.A. (2012). Customer behaviour. Quantitative Problem Solving Methods in the Airline Industry: A Modeling Methodology Handbook. Part of the Fred Hillier International Series on Operations Research and Management Sciences. Vol. 169. Eds. C. Barnhart and B. Smith. New York: Springer. pp. 1-34.
  2. Jacobs, T.L., Garrow, L.A., Lohatepanont, M., Koppelman, F.S., Coldren, G.M. and Purnomo, H. (2012). Airline planning and schedule development. Quantitative Problem Solving Methods in the Airline Industry: A Modeling Methodology Handbook. Part of the Fred Hillier International Series on Operations Research and Management Sciences. Vol. 169. Eds. C. Barnhart and B. Smith. New York: Springer. pp. 35-100.
  3. Southworth, F. and Garrow, L.A. (2011). Travel demand modelling. Wiley Encyclopedia of Operations Research and Management Science. pp. 1-13 DOI: 10.1002/9780470400531. 

PARTS OF BOOKS

  1. Garrow, L.A. and Hotle, S.L. (2017). Airline Passenger Bill of Rights. The SAGE International Encyclopedia of Travel and Tourism.  Ed. L. Lowry. pp. 1-2.
  2. Garrow, L.A. and Hotle, S.L. (2017). Airlines Reporting Company. The SAGE International Encyclopedia of Travel and Tourism.  Ed. L. Lowry. pp. 1-2.
  3. Garrow, L.A. and Hotle, S.L. (2017). Baggage. The SAGE International Encyclopedia of Travel and Tourism.  Ed. L. Lowry. pp. 1-2.
  4. Garrow, L.A. and Hotle, S.L. (2017). In-flight amenities. The SAGE International Encyclopedia of Travel and Tourism.  Ed. L. Lowry. pp. 1-2.
  5. Garrow, L., Hotle, S. and Mumbower, S. (2014). Air travel behavior and research. SAGE Encyclopedia of Transportation: Social Science and Policy. Eds. M. Garrett and J.G. Golson. pp. 1-3.
  6. Garrow, L., Hotle, S. and Mumbower, S. (2014). Airline fares. SAGE Encyclopedia of Transportation: Social Science and Policy. Eds. M. Garrett and J.G. Golson, pp. 1-2.
  7. Garrow, L., Hotle, S. and Mumbower, S. (2014). Airline – service quality modeling. SAGE Encyclopedia of Transportation: Social Science and Policy. Eds. M. Garrett and J.G. Golson. pp. 1-2.

ARTICLES

  1. Garrow, L.A., Mokhtarian, P.L., German, B.J., Glodek, J.S., and Leonard, C.E. (accepted). Market segmentation of an electric vertical takeoff and landing (eVTOL) air taxi commuting service. Transportation Research Part A.
  2. Boddapalli, S.-S., Garrow, L.A., German, B.J., and Newman, J.P. (2024). Mode choice analysis for an electric vertical take-off and landing air taxi commuting service. Transportation Research Part A 181: 104000. https://doi.org/10.1016/j.tra.2024.104000. Dedicated in memory of Robert J. Bowler, father of Laurie A. Garrow.
  3. Garrow, L.A., Lurkin, V., and Marla, L. (2022). Airline innovations soar during COVID-19. Operations Research Forum 3(14): 1-20. https://doi.org/10.1007/s43069-022-00131-1.
  4. Hotle, S., Mumbower, S., and Garrow, L.A. (2022). Highly debated but still debundled: How U.S. airline ancillaries evolved over the last decade. Journal of Revenue and Pricing Management. pp. 18. Published online as of 2022: https://doi.org/10.1057/s41272-022-00388-5.
  5. Rex, J., Ballard, D., Garrow, L., Mills, R.W., and Weingart, D. (2022). A new GIS database documenting the prevalence of U.S. air service development incentives. Journal of Air Transport Management 98: 102148. https://doi.org/10.1016/j.jairtraman.2021.102148.
  6. Roy, S., Kotwicz Herniczek, M.T., Leonard, C., German, B.J., and Garrow, L.A. (2022). Flight scheduling and fleet sizing for an airport shuttle air taxi service. Journal of Air Transportation 30(2): 49-58. https://doi.org/10.2514/1.D0265.
  7. Garrow, L.A. and Lurkin, V. (2021). How COVID-19 is impacting and reshaping the airline industry. Journal of Revenue and Pricing Management 20(1): 3-9. https://doi.org/10.1057/s41272-020-00271-1.
  8. Garrow, L.A., German, B.J., and Leonard, C.E. (2021). Urban air mobility: A comprehensive review and comparative analysis with autonomous and electric ground transportation for informing future research. Transportation Research Part C 132: 103377. https://doi.org/10.1016/j.trc.2021.103377. 
  9. Haan, J., Garrow, L.A., Marzuoli, A., Roy, S., and Bierlaire M. (2021). Are commuter air taxis coming to your city? A ranking of 40 cities in the United States. Transportation Research Part C 132: 103392. https://doi.org/10.1016/j.trc.2021.103392.
  10. Roy, S., Kotwicz Herniczek, M.T., German, B.J., and Garrow, L.A. (2021). User base estimation methodology for a business airport shuttle air taxi service. Journal of Air Transportation 29(2): 69-79. https://doi.org/10.2514/1.D0216.
  11. Vock, S., Garrow, L.A., and Cleophas, C. (2021). Clustering as an approach for creating data-driven perspectives on air travel itineraries. Journal of Revenue and Pricing Management 29(2): 69-79. https://doi-org.prx.library.gatech.edu/10.1057/s41272-021-00323-0.
  12. Garrow, L.A., Chen, Z., Ilbeigi, M., and Lurkin, V. (2020). A new twist on the gig economy: Conducting surveys on Amazon Mechanical Turk. Transportation. 1-20.
  13. Newman, J.P. and Garrow. L.A. (2020). Stacked hybrid discrete choice models for airline itinerary choice. Transportation Research Record 2674(12): 243-253.
  14. Herring, J., Lurkin, V., Garrow, L.A, Clarke, J.P. and Bierlaire, M. (2019). Airline customers’ connection time preferences in domestic U.S. markets. Journal of Air Transport Management, 79: 101688. 
  15. Ilbeigi, M., Lurkin, V. and Garrow, L.A. (2019). Using internet-based marketplaces to conduct surveys: Application to airline itinerary choice models. Transportation Research Part C, 103: 129-141. 
  16. Lurkin, V., Garrow, L.A., Higgins, M.J., Newman, J.P. and Schyns, M. (2018). Modeling competition among airline itineraries. Transportation Research Part A 113: 157-172. 
  17. Newman, J.P., Lurkin, V., and Garrow, L.A. (2018). Computational methods for estimating multinomial, nested, and cross-nested logit models that account for semi-aggregate data. Journal of Choice Modeling 26: 1-13.
  18. Bones, E., Garrow, L.A. and Sturm, T.W. (2017). Incorporating soil erodibility properties into scour risk assessment tools: An application to HYRISK. Journal of Infrastructure Management 23(3): 04016040-1 to 04016040-9 DOI: 10.1061/(ASCE)IS.1943-555X.0000340, 04016040.
  19. Chiew, E., Daziano, R.A. and Garrow, L.A. (2017). Bayesian estimation of hazard models of airline passengers’ cancellation behavior. Transportation Research Part A 96: 154-157. DOI: 10.1016/j.tra.2016.12.006.
  20. Lurkin, V., Garrow, L.A., Higgins, M.J., Newman, J.P. and Schyns, M. (2017). Accounting for price endogeneity in airline itinerary choice models: An application to Continental U.S. markets. Transportation Research Part A 100: 228–246. DOI: 10.1016/j.tra.2017.04.007.
  21. Nicolae, M., Ferguson, M. and Garrow, L. (2016). Measuring the benefit of offering auxiliary services: Do bag-checkers differ in their sensitivities to differences in airline itinerary attributes?  Productions and Operations Management, 25(10): 1689–1708. DOI: 10.1111/poms.12569.
  22. Hotle, S. and Garrow, L.A. (2016). Effects of the traditional and flipped classrooms on undergraduate student opinions and success. ASCE’s Journal of Professional Issues in Engineering Education and Practice, 142(1): pp. 11.  DOI: 10.1061/(ASCE)EI.1943-5541.0000259, 05015005.
  23. Hotle, S., Castillo, M., Garrow, L.A. and Higgins, M.J. (2015). The impact of advance purchase deadlines on airline customers’ search and purchase behaviors. Transportation Research Part A 82:1-16. DOI: 10.1016/j.tra.2015.09.001.
  24. Macfarlane, G., Garrow, L.A. and Mokhtarian, P. (2015). The influences of past and present residential locations on vehicle ownership decisions. Transportation Research Part A 74: 186-200. DOI: 10.1016/j.tra.2015.01.005.
  25. Macfarlane, G., Garrow, L.A. and Moreno-Cruz, J. (2015). Do Atlanta residents value MARTA? Selecting an autoregressive model to recover willingness to pay. Transportation Research Part A 78: 214-230.  DOI: 10.1016/j.tra.2015.05.010. 
  26. Mumbower, S., Garrow, L.A. and Newman, J. (2015). Investigating airline customers’ premium coach seat purchases and implications for optimal pricing strategies. Transportation Research Part A 73: 53-69. DOI: 10.1016/j.tra.2014.12.008.
  27. Penn, R., Garrow, L.A. and Newman, J. (2015). Is your flight really on-time?: An analysis of when U.S. airlines announce flight delays. Transportation Research Record 2471: 73-81. DOI: http://dx.doi.org/10.3141/2471-09.
  28. Binder, S., Macfarlane, G., Garrow, L.A. and Bierlaire, M. (2014). Associations among household characteristics, vehicle characteristics and emission failures: An application of targeted marketing data. Transportation Research Part A 59: 122-133. DOI: 0.1016/ j.tra.2013.11.005.
  29. Hotle, S. and Garrow, L. (2014). The role of competitor pricing on multi-airport search. Transportation Research Record 2400: 21-27. DOI: 10.3141/2400-03.
  30. Katz, D. and Garrow, L.A. (2014). Revenue and operational impacts of depeaking at U.S. hub airports. Journal of Air Transport Management 34(1): 57-64. DOI: 10.1016/ j.jairtraman.2013.07.011.
  31. Kressner, J. and Garrow, L. (2014). Using big data for travel demand modeling: A comparison of targeted marketing, Census, and household travel survey data for Atlanta. Transportation Research Record 2442(1): 8-19. DOI: dx.doi.org/10.3141/2442-02.
  32. Mumbower, S. and Garrow, L.A. (2014). Data set: Online pricing data from multiple U.S. carriers. Manufacturing and Service Operations Management 16(2): 198-203. DOI: 10.1287/msom.2013.0466.
  33. Mumbower, S., Garrow, L.A. and Higgins, M.J. (2014). Estimating flight-level price elasticities using online airline data: A first step towards integrating pricing, demand, and revenue optimization. Transportation Research Part A 66: 196–212.  DOI: 10.1016/j.tra.2014.05.003.
  34. Newman, J.P., Ferguson, M.E., Garrow, L.A. and Jacobs, T. (2014). Estimation of choice-based models using sales data from a single firm. Manufacturing and Service Operations Management 16(2): 184-197. DOI: 10.1287/msom.2014.0475.
  35. Katz, D. and Garrow, L. (2013). Depeaking schedules: Beneficial for airports and airlines? Transportation Research Record 2325: 43-55. DOI: dx.doi.org/10.3141/2325-05.
  36. Khelifa, A., Garrow, L.A., Higgins, M.J. and Meyer, M.D. (2013). The impacts of climate change on scour-vulnerable bridges: An assessment based on HYRISK. ASCE Journal of Infrastructure Systems 19(2): 138-146. DOI: 10.1061/(ASCE)IS.1943-555X.0000109.
  37. Newman, J.P., Ferguson, M.E. and Garrow, L.A. (2013). Estimating GEV models with censored data. Transportation Research Part B 58: 170-184. DOI: 10.1016/ j.trb.2013.09.002.
  38. Newman, J.P., Ferguson, M.E. and Garrow, L.A. (2013). Estimating nested logit models with censored data. Transportation Research Record 2343: 62-67. DOI: 10.3141/2343-08.
  39. Ferguson, M.E., Garrow, L.A. and Newman, J.P. (2012). Application of discrete choice models to choice-based revenue management problems: A cautionary note. Journal of Revenue and Pricing Management 11(5): 536-547. DOI: 10.1057/rpm.2011.38.
  40. Garrow, L.A., Hotle, S. and Mumbower, S. (2012). Assessment of product debundling trends in the U.S. airline industry: Customer service and public policy implications. Transportation Research Part A 46(2): 255-268. DOI: 10.1016/j.tra.2011.09.009.
  41. Katz, D. and Garrow, L.A. (2012). The impacts of door crowding on operations and safety for private buses in a developing country. Journal of Public Transportation 15(2): 43-65.
  42. Kressner, J. and Garrow, L.A. (2012). Using lifestyle variables to predict home-based trips to Hartsfield-Jackson Atlanta airport. Transportation Research Record 2266: 20-30. DOI: 10.3141/2266-03.
  43. Lee, M., Khelifa, A., Garrow, L., Bierlaire, M. and Post, D. (2012). An analysis of destination choice for opaque airline products using multidimensional binary logit models. Transportation Research Part A 46(10): 1641–1653. DOI: 10.1016/j.tra.2012.08.009.
  44. Newman, J., Ferguson, M. and Garrow, L. (2012). Estimating discrete choice models with incomplete data. Transportation Research Record 2302: 130-137. DOI: 10.3141/2302-14.
  45. Fragaszy, R.J., Santamarina, J.C., Amekudzi, A., Assimaki, D., Bachus, R., Burns, S.E., Cha, M.S., Cho, G.C., Cortes, D.D., Dai, S., Espinoza, D.N., Garrow, L., Huang, H., Jung, J.W., Kim, S.H., Kurtis, K., Lee, C.H., Pasten, C.R., Phadnis, H., Rix, G., Shin, H.S., Torres, M.C., Touris, C. (2011). Sustainability: Potential roles for geotechnical engineering, KSCE Journal of Civil Engineering 15(4): 611-621. DOI: 10.1007/s12205-011-0102-7.
  46. Garrow, L.A., Kressner, J. and Mumbower, S. (2011). Is increasing airline denied boarding compensation limits the answer?: A review of factors that contribute to denied boardings. Journal of Air Transport Management 17(5): 271-277. DOI: 10.1016/ j.jairtraman.2011.03.002.
  47. Lee, S., Garrow, L.A., Higbie, J.A., Keskinocak, P. and Koushik, D. (2011). Do you really know who your customers are?: A study of U.S. retail hotel demand. Journal of Revenue and Pricing Management 10(1): 73-86. DOI: 10.1057/rpm.2009.8.
  48. Luken, B. and Garrow, L.A. (2011). Multi-airport choice models for the New York metropolitan area based on ticketing data. Transportation Research Record 2206: 24-31. DOI: 10.3141/2206-04.
  49. Garrow, L.A., Bodea, T.D. and Lee, M. (2010). Generation of synthetic datasets for discrete choice analysis. Transportation 37(2): 183-202. DOI: 10.1007/s11116-009-9228-6.
  50. Graham, R.J., Garrow, L.A. and Leonard, J.D. (2010). Business travelers’ refund and exchange behavior. Journal of Air Transport Management 16(4): 196-201. DOI: 10.1016/ j.jairtraman.2009.12. 002.
  51. Mumbower, S. and Garrow, L.A. (2010). Using online data to explore competitive airline pricing policies: A case study approach. Transportation Research Record 2184: 1-12. DOI: 10.3141/2184-01.
  52. Bodea, T.D., Ferguson, M.E. and Garrow, L.A. (2009). Choice-based revenue management: Data from a major hotel chain. Manufacturing and Service Operations Management 11(2): 356-361. DOI: 10.1287/msom.1080.0231.
  53. Bodea, T.D., Garrow, L.A., Meyer, M.D. and Ross, C.L. (2009). Socio-demographic and built environment influences on the odds of being overweight or obese: The Atlanta experience. Transportation Research Part A 43(4): 430-444. DOI: 10.1016/ j.tra.2008.11.009.
  54. Garrow, L.A. (2009). Online travel data: A goldmine of new opportunities. Journal of Revenue and Pricing Management 8(2/3): 247-254. DOI: 10.1057/rpm.2008.55.
  55. Pope, S., Garrow, L., Guin, A., Leonard, J., Bankston, L. and Campbell, P. (2009). A conceptual framework for collecting online airline pricing data: Challenges, opportunities, and preliminary results. Transportation Research Record 2016: 30-37. DOI: 10.3142/2106-04.
  56. Bodea, T.D., Garrow, L.A., Meyer, M.D. and Ross, C.L. (2008). Explaining obesity with urban form: A cautionary tale. Transportation 35(2): 179-199. DOI: 0.1007/s11116-007-9148-2.
  57. Iliescu, D.C., Garrow, L.A. and Parker, R.A. (2008). A hazard model of U.S. airline passengers’ refund and exchange behavior. Transportation Research Part B 42(3): 229-242. DOI: 10.1016/j.trb.2007.10.005.
  58. Garrow, L.A., Jones, S.P. and Parker, R.A. (2007). How much airline customers are willing to pay: An analysis of price sensitivity in online distribution channels. Journal of Revenue and Pricing Management 5(4): 271-290. DOI: 10.1057/palgrave.rpm.5160052.
  59. Garrow, L.A., Koppelman, F.S. and Nelson, B.L. (2005). Efficient estimation of nested logit models using choice-based samples. In proceedings of the 16th International Symposium on Transportation and Traffic Theory: Transportation and Traffic Theory: Flow, Dynamics, and Human Interactions, University of Maryland, College Park, July 19-21. Ed. Hani S. Mahmassani: 525-544.
  60. Koppelman, F.S. and Garrow, L.A. (2005). Efficiently estimating nested logit models with choice-based samples: Example applications. Transportation Research Record 1921: 63-69. DOI: 10.3141/1921-08.
  61. Garrow, L.A. and Koppelman, F.S. (2004). Multinomial and nested logit models of airline passengers’ no-show and standby behavior. Journal of Revenue and Pricing Management 3(3): 237-253. DOI: 10.1057/palgrave.rpm.5170111.
  62. Garrow, L.A. and Koppelman, F.S. (2004). Predicting air travelers’ no-show and standby behavior using passenger and directional itinerary information. Journal of Air Transport Management 10(6): 401-411. DOI: 10.1016/j.jairtraman.2004.06.007.

CONFERENCE PROCEEDING (NON-REFERRED)

  1. Garrow, L.A., German, B.J., Schwab, N.T., Patterson, M.D., Mendonca, N.L., Gawdiak, Y.O. and Murphy, J.R. (2022). A proposed taxonomy for advanced air mobility. In proceedings from the American Institute of Aeronautics and Astronautics, Chicago, IL, pp. 25. Click here for pre-print. 
  2. Hill, C. and Garrow, L.A. (2021). A market segmentation analysis for an eVTOL air taxi shuttle. In proceedings from the American Institute of Aeronautics and Astronautics Sci-Tech Forum, virtual event, pp. 18. Click here for pre-print.
  3. Leonard, C.E., Garrow, L.A., and Newman, J.P. (2021). A survey to model demand for eVTOL trips to airports. In proceedings from the American Institute of Aeronautics and Astronautics Sci-Tech Forum, virtual event, pp. 48. Click here for pre-print. 
  4. Roy, S., Kotwicz Herniczek, M.T., Leonard, C., Jha, A., Wang, N., German, B.J., and Garrow, L.A. (2020). A multi-commodity network flow approach for optimal flight scheduling of an airport shuttle air taxi service. In proceedings from the American Institute of Aeronautics and Astronautics Sci-Tech Forum, Orlando, Florida. pp. 1-19. Click here for pre-print.
  5. Garrow, L.A., Mokhtarian, P.L., German, B.J., and Boddapalli, S.-S. (2020). Commuting in the age of the Jetsons: A market segmentation analysis of autonomous ground vehicles and air taxis in five large U.S. cities. In proceedings from the American Institute of Aeronautics and Astronautics, Reno, Nevada:  pp. 1-18. Click here for pre-print.
  6. Garrow, L.A., Mokhtarian, P., German, B.J., Glodek, J. and Boddupalli S.-S. (2019). A survey to model demand for eVTOL urban air trips and competition with autonomous ground vehicles. pp. 1-45. Click here for pre-print. 
  7. Kotwicz Herniczek, M.T., Garbo, A., Lau, M., German, B.J. and Garrow, L.A. (2019). Exploration of near-term urban air mobility operations with retrofitted electric general aviation aircraft. In proceedings from the American Institute of Aeronautics and Astronautics, Dallas, TX. pp. 1-18.  Click here for pre-print. 
  8. Daskilewicz, M.J., German, B J., Warren, M.M., Garrow, L.A., Boddupalli S.-S. and Douthat, T.D. (2018). Progress in vertiport placement and estimating aircraft range requirements for eVTOL daily commuting. In proceedings from the American Institute of Aeronautics and Astronautics, Atlanta, GA. pp. 1-10.  Click here for pre-print. 
  9. Binder, R., Garrow, L.A., German, B.J., Mokhtarian, P., Daskilewicz, M.J. and Douthat, T.D. (2018). If you fly it, will commuters come?  Predicting demand for eVTOL urban air trips. In proceedings from the American Institute of Aeronautics and Astronautics, Atlanta, GA. pp. 1-41. Click here for pre-print. 
  10. Garrow, L.A., Ilbeigi, M., and Chen, Z. (2017). Forecasting demand for on demand mobility. In proceedings from the American Institute of Aeronautics and Astronautics, Denver, CO. pp. 1-7.  Click here for pre-print.
  11.  Iliescu, D.C., Garrow, L.A. and Parker, R.A. (2006). Analysis of U.S. airline passengers’ refund and exchange behavior across multiple carriers. In proceedings from the European Transport Conference, Strasbourg, France. pp. 1-28.
  12.  Bodea, T.D. and Garrow, L.A. (2006). The importance of synthetic datasets in empirical testing: Comparison of NL and MNL with error components models. In proceedings from the European Transport Conference, Strasbourg, France. pp. 1-25.
  13. Garrow, L.A. and Bodea, T.D. (2005). A rigorous framework for empirically comparing mixed GEV and mixed MNL with error components models. In proceedings from the European Transport Conference, Strasbourg, France. pp. 1-20. 

OTHER PUBLICATIONS

  1. Franz, J.D., Holbert, H., Garrow, L.A., Gosling, G.D., Vande Kamp, M., Harmon, L., and Ward, S. (2021). Guidebook for Conducting Airport User Surveys and Other Customer Research.  Airport Cooperative Research Report 235. Washington, DC: National Academies. pp. 242 DOI: 10.17226/26444.
  2. Garrow, L.A., Lavanya, M., and Clarke, J.P. (2021, February 2). Airline response to COVID-19 and beyond. OR/MS Today. 30-33. Available online here.
  3. Garrow, L.A., Irrgang, M., and Semar, J. (2020, August). The first 100 days: How airlines responded to the COVID-19 crisis. Avionics International. Available online here.
  4. Ballard, D., Weingart, D., Garrow, L., Herring, J., Mills, R.W., Burns, W., Rex, J.M., Caniglia, M. (2020).  Building and Maintaining Air Service Through Incentive Programs. Airport Cooperative Research Report 218. Washington, DC: National Academies. pp. 54. DOI 10.17226/25758.
  5. Ballard, D., Garrow, L.A., and Gosling, G.D. (2019). Using Disaggregate Socioeconomic Data in Air Passenger Demand Studies. Airport Cooperative Research Report 194. Washington, DC: National Academies. pp. 134. DOI 10.17226/25411.
  6. Cochran, J., Garrow, L.A, and Nord, A. (2017). The “trending urban” shift in rural transit.  MTAP Network News: AASHTO Multi-State Transit Technical Assistance Program. Summer-Fall: 6.
  7. Hotle, S. and Garrow, L.A. (2015). Flipped and micro-flipped classrooms. OR/MS Today 42(1): 12-13.
  8. Garrow, L.A., Hotle, S. and Mumbower, S. (2013). Investigating student learning and attitudes in a switched-role, interactive environment. OR/MS Today 40(4): 10.