Ett informationsblad från matematiska institutionen vid Linköpings universitet
v25 1997
Föreläsningar
Seminarium i optimeringslära
Torsdag den 19 juni kl 10.15 talar Marielle Christiansen, Section of Managerial Economics and Operations Research Norwegian University of Science and Technology Trondheim, Norge, om Inventory and Time Constrained Ship Routing
Abstract:
We have studied a new type of routing problem, which is a combined pickup and delivery problem with time windows and an inventory management problem: The Inventory Pickup and Delivery Problem with Time Windows - IPDPTW.
The research is motivated by a real ship planning problem for ammonia distribution in Europe. It involves the design of a set of minimum cost routes for a fleet of heterogeneous ships which service a set of harbours one or more times during the planning period. The production and inventory information at each harbour, together with the ship capacities and the location of the harbours, determine the number of possible visits at each harbour, the time windows for start of service and the load quantity intervals at each visit. The production at the harbours are continuous, and the ships transport the product from production harbours to consumption harbours.
In the mathematical programming model, we duplicate the start time and load quantity variables and use a Dantzig-Wolfe decomposition approach. Then the IPDPTW decomposes into a subproblem for each harbour and a subproblem for each ship. For each harbour, the harbour subproblem ensures the inventory will be within the stock limits during the planning period. Normally, there exist several feasible combinations of load quantities, start times and number of visits at a harbour during the planning period, and we call each of then a harbour visit sequence. The ship subproblem for a ship finds feasible routes with regard to the time windows and the quantity on board the ship. The master problem ensures that the number of visits to a harbour is within a calculated limit. In addition, it includes coupling constraints for the start times and load quantities to synchronize the harbour inventory and ship route aspects.
According to the Dantzig-Wolfe column generation approach, the master problem is solved iteratively until no new promising columns, representing ship routes or harbour visit sequences, can be generated. These columns are generated by solving the subproblems by specific dynamic programming algorithms. The subproblems' cost functions are piecewise linear and non-increasing over the start time, due to continuously declared start times and dual information from the time coupling constraints in the master problem. Finally, this iterative solution process is embedded in a branch-and-bound search to make the solution integer optimal.
Lokal: MAI:s seminarierum, Kompakta rummet
Välkomna!
Gästföreläsning
Torsdagen den 19 juni kl. 10.15-11.15 talar Jarmila Ranosová om Sets of determination in potential theory.
Abstract:
For a ball D (or a more general domain) in 
,
a given strictly positive harmonic function 
and
a class 
of harmonic functions on D,
a set M is called a set of determination with respect to 
and 
, if
for all functions in 
.
A survey of classical results of sets of determination
and some of my results about sets of determination in the
case of the heat equation and the Helmholtz equation will be given.
The problem of characterizing sets of determination in the classical case has been studied by many authors.
In my talk sets of determination will be characterized for parabolic functions, i. e. solutions of the heat equation, and for solutions of more general parabolic equations, on a slab. The situation is different, as in view of the anisotropic character of the parabolic equation, only one-sided Harnack inequality is available. Sets of determination with respect to u, a positive upper bounded parabolic function, and a class of positive parabolic functions will be described; cf. [1], [2].
The case of the Helmholtz equation on 
is considered, too;
see [3].
As an application certain
decomposition theorems
of functions belonging to 
are given.
Lokal: MAI:s seminarierum Beurling
Välkomna!
Jana och Anders Björn
Personalinformation
Karin Johansson är förordnad som vikarierande administrativ assistent i matematisk statistik.
Marthina Flogén nedkom i lördags med en pojke.
Kort från institutionsstyrelsens sammanträde 97-06-11
Tjänster:
En arvodestjänst som
gästforskare inrättades för Prof. Tuy under tiden 1/8-15/10-97.
Två doktorandtjänster i tillämpad matematik inrättades.
Dragu Atanasiu och Bengt Ove Turesson har erhållit var sitt långtidsvikariat som universitetslektor i matematik.
Som vik univ.lektor i matematisk statistik utsågs Ann-Marie Flygare. Hon förordnades även på tjänsten som univ.adjunkt i matematisk statistik.
Verksamhetsplanerna för 97/98 samt utseende av examinatorer presenterades av ämnenas studierektorer.
Intendenten informerade om budgeten för verksamhetsåret 97/98.
Under övriga ärenden redogjorde Linde Wittmeyer-Koch för matematikerprogrammet och Lars Eldén informerade om att Tomas Larsson och Peter Värbrand flyttar över sina tjänster till Norrköping.
Delegerades till prefekten att fatta beslut under sommarupphållet.
Höstens första sammanträde blir 24 september.
Birgitta Lumsden
Tack!!
till Jana, Jan O, Erland, Mikael H och Tatyana för den trevliga
vårutflykten
som i år gick till Ekenäs slott, Thorslunds tunnbinderi och Mormorsgruvan.
Lite Mat tar nu semester och
återkommer vecka 33
GLAD SOMMAR!
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Material till Lite Mat lämnas till Maud Lindström senast
torsdagar kl 12.00.
Tel 013-281405, Fax 013-100746, Email: litemat@mai.liu.se
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