Department of Computer Science | Institute of Theoretical Computer Science | CADMO

Prof. Emo Welzl and Prof. Bernd Gärtner

Mittagsseminar Talk Information |

**Date and Time**: Tuesday, February 17, 2004, 12:15 pm

**Duration**: This information is not available in the database

**Location**: This information is not available in the database

**Speaker**: Alexander Hall

Flow variation over time is an important feature in network flow
problems arising in various applications such as road or air traffic
control, production systems, communication networks (e.g., the
Internet), and financial flows. The common characteristic are
networks with capacities and transit times on the edges which specify
the amount of time it takes for flow to travel through a particular
edge. Moreover, in contrast to static flow problems, flow values on
edges may change with time in these networks.

I will give a short introduction to the flows over time problem and
mention new complexity and inapproximability results for the case
where the transit times are assumed to be constant.

In many real-world applications transit times are not constant but
depend on the current flow situation in the network. For the model
where the transit time of an edge is given as a nondecreasing function
of the rate of inflow into the edge I will present the ideas
underlying an FPTAS for the `quickest multicommodity flow problem with
bounded cost'. It can be shown that this problem is NP-hard even in
the single commodity case.

This is joint work with Steffen Hippler, Katharina Langkau, and Martin Skutella.

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