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Levén, Erik
Publications (8 of 8) Show all publications
Segerstedt, A. & Levén, E. (2014). A study of different Croston-like forecasting methods (ed.). Paper presented at . Luleå
Open this publication in new window or tab >>A study of different Croston-like forecasting methods
2014 (English)Report (Other academic)
Abstract [en]

Croston (1972) presented an idea and method to separate ordinary exponential smoothing in two parts; in the time between demand, or withdrawals, and demand size. The forecasts are then updated only when there is a demand. Syntetos and Boylan (2005) recommended an adjustment of the Croston method due to a systematic error notified by Syntetos and Boylan (2001). Levén and Segerstedt (2004) suggested a modification of the Croston method where a demand rate is directly calculated when a demand has happened. In this paper real demand data is used to compare these variants of the Croston method. The idea with the modification of Levén and Segerstedt (2004) is that time between demand and demand size is not independent. But this modification has shown poor results. Therefore Wallström and Segerstedt (2010) suggest another modification, a “forward coverage” different to the previous “backward coverage”. Teunter et al (2011) suggest another method, a combination of updates every time period, for estimating the probability of a demand occasion, and every time a demand occurs for estimating demand size. All these different techniques are tested here. The different tech-niques are compared with Mean Squared Error (MSE), Cumulated Forecast Error (CFE) and with the new bias measure “Periods in Stock” (PIS). The tests show that modified Croston with “forward cover-age” in most cases seems to be to prefer compared to “backward coverage”, but still it overestimates demand. Ordinary Croston may be to prefer; therefore our tests show that Croston according to Syntetos and Boylan and also Teunter et al show a tendency to underestimate demand.

Place, publisher, year, edition, pages
Luleå: , 2014. p. 18
National Category
Production Engineering, Human Work Science and Ergonomics
Research subject
Industrial Logistics
Identifiers
urn:nbn:se:ltu:diva-24548 (URN)b690cae1-d468-4566-b375-db8c5dfe106a (Local ID)b690cae1-d468-4566-b375-db8c5dfe106a (Archive number)b690cae1-d468-4566-b375-db8c5dfe106a (OAI)
Note
Godkänd; 2014; 20140206 (ysko)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-04-10Bibliographically approved
Levén, E. & Segerstedt, A. (2012). Study of different variants of Croston forecasting methods (ed.). Paper presented at International Working Seminar on Production Economics : 20/02/2012 - 24/02/2012. Paper presented at International Working Seminar on Production Economics : 20/02/2012 - 24/02/2012.
Open this publication in new window or tab >>Study of different variants of Croston forecasting methods
2012 (English)Conference paper, Oral presentation only (Refereed)
National Category
Production Engineering, Human Work Science and Ergonomics
Research subject
Industrial Logistics
Identifiers
urn:nbn:se:ltu:diva-28461 (URN)245752a4-05ef-4bb8-96b6-b0a9f17697e7 (Local ID)245752a4-05ef-4bb8-96b6-b0a9f17697e7 (Archive number)245752a4-05ef-4bb8-96b6-b0a9f17697e7 (OAI)
Conference
International Working Seminar on Production Economics : 20/02/2012 - 24/02/2012
Note
Godkänd; 2012; 20120326 (ysko)Available from: 2016-09-30 Created: 2016-09-30 Last updated: 2018-04-10Bibliographically approved
Levén, E. & Segerstedt, A. (2007). A scheduling policy for adjusting economic lot quantities to a feasible solution (ed.). Paper presented at . European Journal of Operational Research, 179(2), 414-423
Open this publication in new window or tab >>A scheduling policy for adjusting economic lot quantities to a feasible solution
2007 (English)In: European Journal of Operational Research, ISSN 0377-2217, E-ISSN 1872-6860, Vol. 179, no 2, p. 414-423Article in journal (Refereed) Published
Abstract [en]

A heuristic scheduling policy is introduced for a multi-item, single-machine production facility. The scheduling policy uses the presumed optimal order quantities derived from solving an Economic Lot Size Problem and checks that the quantities obtain a feasible production schedule according to current inventory levels and expected demand rates. If not, the scheduling policy modifies the order quantities to achieve a possible solution without shortages. The scheduling policy is inspired by modification of the similar heuristic Dynamic Cycle Lengths Policy by Leachman and Gascon from 1988, 1991. The main characteristics of this scheduling policy are successive batches of the same item are treated explicitly, due to that it is quite possible that one item be manufactured several times before one other item is manufactured once more; the batches are ordered in increasing run-out time; if the existing situation creates stock-outs with ordinary order quantities, then the order quantities are decreased with a common scaling factor to try to prevent inventory shortages; in case the decrease of the order quantities changes expected run-out times, the batches are reordered after new run-out times; no filling up to an explicit inventory level is done, the filling up is done by the desirable order quantity; to prevent possible excess inventory the policy suggests time periods where no production should be performed. The scheduling policy contains no economical evaluation; this is supposed to be done when the order quantities are calculated, the policy prevents shortages and excess inventory. A numerical example illustrates the suggested scheduling policy. Finally, it is discussed as to how the policy can also take into account stochastic behaviour of the demand rates and compensate the schedule by applying appropriate safety times.

National Category
Production Engineering, Human Work Science and Ergonomics
Research subject
Industrial Logistics
Identifiers
urn:nbn:se:ltu:diva-10229 (URN)10.1016/j.ejor.2006.03.038 (DOI)000243292800010 ()2-s2.0-33751407199 (Scopus ID)8fe89cf0-8d53-11db-8975-000ea68e967b (Local ID)8fe89cf0-8d53-11db-8975-000ea68e967b (Archive number)8fe89cf0-8d53-11db-8975-000ea68e967b (OAI)
Note
Validerad; 2007; 20061117 (ysko)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Brander, P., Levén, E. & Segerstedt, A. (2005). Lot sizes in a capacity constrained facility: a simulation study of stationary stochastic demand (ed.). Paper presented at . International Journal of Production Economics, 93-94(Spec. issue), 375-386
Open this publication in new window or tab >>Lot sizes in a capacity constrained facility: a simulation study of stationary stochastic demand
2005 (English)In: International Journal of Production Economics, ISSN 0925-5273, E-ISSN 1873-7579, Vol. 93-94, no Spec. issue, p. 375-386Article in journal (Refereed) Published
Abstract [en]

This paper considers the scheduling of several different items on a single machine, in literature known as the economic lot scheduling problem, ELSP. One of the characteristics of this problem is that the demand rate is deterministic and constant. However, in a practical situation demand usually varies. In this paper we examine if a deterministic model can be used if demand is stationary stochastic. A dynamic programming approach from Bomberger (Manage. Sci. 12(11) (1966) 778) and a heuristic method from Segerstedt (Int. J. Production Econom. 59(1–3) (1999) 469) are used to calculate lot sizes for four items. The production of these items is simulated with different variations in demand rates. Our conclusion is that a deterministic model of this kind can be used in a practical situation where the demand rate is stationary stochastic, but the models must be complemented by a decision rule; which item to produce and when to produce it. In our tests the heuristic method and the dynamic programming approach perform rather similarly with respect to costs and inventory levels, but the dynamic programming approach results in more backorders when there is small variation in demand rates. This study indicates that the model used for determination of lot sizes is of less importance than the decision rule used for identification of the item to produce and when to produce it.

National Category
Production Engineering, Human Work Science and Ergonomics
Research subject
Industrial Logistics
Identifiers
urn:nbn:se:ltu:diva-15966 (URN)10.1016/j.ijpe.2004.06.034 (DOI)000225423600036 ()2-s2.0-9544253909 (Scopus ID)f8d59f70-7637-11db-962b-000ea68e967b (Local ID)f8d59f70-7637-11db-962b-000ea68e967b (Archive number)f8d59f70-7637-11db-962b-000ea68e967b (OAI)
Note
Validerad; 2005; Bibliografisk uppgift: Proceedings of the Twelfth International Symposium on Inventories; 20061117 (ysko)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Levén, E. & Segerstedt, A. (2004). Inventory control with a modified Croston procedure and Erlang distribution (ed.). Paper presented at . International Journal of Production Economics, 90(3), 361-367
Open this publication in new window or tab >>Inventory control with a modified Croston procedure and Erlang distribution
2004 (English)In: International Journal of Production Economics, ISSN 0925-5273, E-ISSN 1873-7579, Vol. 90, no 3, p. 361-367Article in journal (Refereed) Published
Abstract [en]

This paper considers an inventory control system, primarily for a finished goods inventory. The purpose is to create a procedure that can handle both fast-moving items with regular demand and slow-moving items. The suggested procedure should be easy to implement in a modern computerized ERP-system. Essentially, the system is a periodic review system built around a Croston forecasting procedure. An Erlang distribution is fitted to the observed data using the mean and variance of the forecasted demand rate. According to probabilities for stock shortages, derived from the probability distribution, the system decides if it is time to place a new order or not. The Croston forecasting method is theoretically more accurate than ordinary exponential smoothing for slow-moving items. However, it is not evident that a Croston forecasting procedure (with assumed Erlang distribution) outperforms ordinary exponential smoothing (with assumed normal distribution) applied in a “practical” inventory control system with varying demand, automatically generated replenishment, etc. Our simulation study shows that the system in focus will present fewer shortages at lower inventory levels than a system based on exponential smoothing and the normal distribution.

National Category
Production Engineering, Human Work Science and Ergonomics
Research subject
Industrial Logistics
Identifiers
urn:nbn:se:ltu:diva-12955 (URN)10.1016/S0925-5273(03)00053-7 (DOI)000222538000006 ()2-s2.0-2942642468 (Scopus ID)c1bd1750-7639-11db-962b-000ea68e967b (Local ID)c1bd1750-7639-11db-962b-000ea68e967b (Archive number)c1bd1750-7639-11db-962b-000ea68e967b (OAI)
Note
Validerad; 2004; 20061117 (ysko)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Brander, P., Levén, E. & Segerstedt, A. (2004). Lot sizes in a capacity constrained facility: a simulation study of stationary stochastic demand (ed.). In: (Ed.), Attila Chikan (Ed.), Proceedings of the Twelth International Symposium on Inventories: [... held in Budapest, Hungary on August 20 - 25, 2002]. Paper presented at International Symposium on Inventories : 20/08/2002 - 25/08/2002. Amsterdam: Elsevier
Open this publication in new window or tab >>Lot sizes in a capacity constrained facility: a simulation study of stationary stochastic demand
2004 (English)In: Proceedings of the Twelth International Symposium on Inventories: [... held in Budapest, Hungary on August 20 - 25, 2002] / [ed] Attila Chikan, Amsterdam: Elsevier, 2004Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
Amsterdam: Elsevier, 2004
National Category
Production Engineering, Human Work Science and Ergonomics
Research subject
Industrial Logistics
Identifiers
urn:nbn:se:ltu:diva-29652 (URN)33101890-7819-11db-962b-000ea68e967b (Local ID)33101890-7819-11db-962b-000ea68e967b (Archive number)33101890-7819-11db-962b-000ea68e967b (OAI)
Conference
International Symposium on Inventories : 20/08/2002 - 25/08/2002
Note
Godkänd; 2004; 20061119 (ysko)Available from: 2016-09-30 Created: 2016-09-30 Last updated: 2018-04-10Bibliographically approved
Levén, E. & Segerstedt, A. (2004). Polarica’s wild berries: an example of a required storage capacity calculation and where to locate this inventory (ed.). Paper presented at . Supply chain management, 9(3), 213-218
Open this publication in new window or tab >>Polarica’s wild berries: an example of a required storage capacity calculation and where to locate this inventory
2004 (English)In: Supply chain management, ISSN 1359-8546, E-ISSN 1758-6852, Vol. 9, no 3, p. 213-218Article in journal (Refereed) Published
Abstract [en]

Polarica is a company in northern Europe buying, refining and selling wild berries and other specialty foods. During the last couple of years the volume of wild berries, mostly blueberries, has increased a lot. This expansion forces Polarica to consider investments in freezing-in capacity and cold-storage capacity. A simple heuristic model was constructed, from which it was concluded that additional volumes of frozen blueberries require more storage facilities and it was also recommended that the location should be based on load-distance analysis. The way this problem is tackled and solved can be copied and hopefully it presents ideas for other similar studies.

National Category
Production Engineering, Human Work Science and Ergonomics
Research subject
Industrial Logistics
Identifiers
urn:nbn:se:ltu:diva-5633 (URN)10.1108/13598540410544908 (DOI)000224059200002 ()2-s2.0-9444277852 (Scopus ID)3c972f00-764a-11db-962b-000ea68e967b (Local ID)3c972f00-764a-11db-962b-000ea68e967b (Archive number)3c972f00-764a-11db-962b-000ea68e967b (OAI)
Note
Validerad; 2004; 20061117 (ysko)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Levén, E. (2003). A heuristic scheduling policy for the economic lot scheduling problem with stochastic demand (ed.). Paper presented at EURO/INFORMS Joint International Meeting : 06/07/2003 - 10/07/2003. Paper presented at EURO/INFORMS Joint International Meeting : 06/07/2003 - 10/07/2003.
Open this publication in new window or tab >>A heuristic scheduling policy for the economic lot scheduling problem with stochastic demand
2003 (English)Conference paper, Oral presentation only (Refereed)
National Category
Production Engineering, Human Work Science and Ergonomics
Research subject
Industrial Logistics
Identifiers
urn:nbn:se:ltu:diva-37215 (URN)b2b3bca0-78e1-11db-962b-000ea68e967b (Local ID)b2b3bca0-78e1-11db-962b-000ea68e967b (Archive number)b2b3bca0-78e1-11db-962b-000ea68e967b (OAI)
Conference
EURO/INFORMS Joint International Meeting : 06/07/2003 - 10/07/2003
Note
Godkänd; 2003; 20061119 (ysko)Available from: 2016-10-03 Created: 2016-10-03 Last updated: 2017-11-25Bibliographically approved
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