The minimum speed for a blocking problem on the half plane

Alberto Bressan, Tao Wang

Research output: Contribution to journalArticlepeer-review

13 Scopus citations


We consider a blocking problem: fire propagates on a half plane with unit speed in all directions. To block it, a barrier can be constructed in real time, at speed σ. We prove that the fire can be entirely blocked by the wall, in finite time, if and only if σ > 1. The proof relies on a geometric lemma of independent interest. Namely, let K ⊂ R2 be a compact, simply connected set with smooth boundary. We define dK (x, y) as the minimum length among all paths connecting x with y and remaining inside K. Then dK attains its maximum at a pair of points (over(x, ̄), over(y, ̄)) both on the boundary of K.

Original languageEnglish (US)
Pages (from-to)133-144
Number of pages12
JournalJournal of Mathematical Analysis and Applications
Issue number1
StatePublished - Aug 1 2009

All Science Journal Classification (ASJC) codes

  • Analysis
  • Applied Mathematics


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