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Buffons nålproblem och dess generalisering: Från klassisk sannolikhet till integralgeometri
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electrical Engineering, Mathematics and Science.
2025 (Swedish)Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
Abstract [sv]

Detta arbete behandlar ett av de äldsta exemplen på geometrisk sannolikhet, nämligen Buffons klassiska nålproblem samt dess generalisering till högre dimensioner. Utifrån ett modernt matematiskt perspektiv undersöks problemet både analytiskt och geometriskt, med betoning på symmetrier, sannolikhetsmått och integralgeometriska verktyg. Arbetet inleds med en formell härledning av sannolikheten att en nål korsar ett system av parallella linjer i planet. Där undersöks både det klassiska fallet (L<D) och det mer generella (L≥D).

Genom att tillämpa sannolikhetsteori, måtteoretiska principer och geometriska symmetrier, reduceras problemet till ett tvådimensionellt integraluttryck. Parallellt presenteras en alternativ geometrisk lösning som bygger på linjäritetsegenskaper hos förväntade värden. Denna tolkning leder vidare till en approximation π med hjälp av Monte Carlo-metoder, där simulering kombineras med felanalys.

I arbetets senare del generaliseras Buffons nålproblem till det n-dimensionella euklidiska rummet. Där kastas slumpmässigt en godtycklig kompakt konvex kropp mot ett gitter av parallella k-dimensionella underrum. Denna generalisering kräver en djupare förståelse av geometrisk sannolikhetsteori, gitterteori och måtteori. Med hjälp av integralgeometrins kinematiska formler visas att det förväntade antalet korsningar kan uttryckas i termer av intrinsiska volymer, vilket knyter samman kroppens geometri med sannolikhetens symmetriska struktur.

Arbetet visar hur ett synnerligen grundläggande sannolikhetsproblem leder vidare till avancerade begrepp inom modern geometri och analys. Genom att kombinera rigorösa analytiska metoder med geometriska och sannolikhetsteoretiska insikter visar arbetet hur klassisk sannolikhet kan leda till högdimensionell integralgeometri.

Abstract [en]

This thesis examines one of the oldest examples of geometric probability, namely Buffon's classical needle problem, along with its generalization to higher dimensions. From a modern mathematical perspective, the problem is analyzed both analytically and geometrically, with emphasis on symmetries, probability measures and tools from integral geometry. The work begins with a formal derivation of the probability that a needle intersects a system of parallel lines in the plane. Where both the classical case (L<D) and the more general scenario (L≥D) are covered.

By applying probability theory, measure-theoretic methods and  geometric symmetries, the problem is reduced to a two-dimensional integral expression. In parallel, an alternative geometric solution is presented, based on linearity properties of expected values. This interpretation is extended to approximate the value of π via Monte Carlo-methods, combining simulation with statistical error analysis.

In the latter part of the thesis, Buffon's needle problem is generalized to the n-dimensional Euclidean space, where a randomly placed compact convex body intersects a lattice of parallel k-dimensional subspaces. This generalization requires a deeper understanding of geometric probability, lattice theory and measure theory. Using kinematic formulas from integral geometry, it is shown that the expected number of intersections can be expressed in terms of intrinsic volumes, thereby linking the geometry of the body to the symmetry structure of the probability measure.

The thesis demonstrates how a seemingly elementary probability problem gives rise to advanced concepts in modern geometry and analysis. By combining rigorous analytical methods with geometric and probabilistic insight, it highlights how classical probability naturally leads into the realm of high-dimensional integral geometry.

Place, publisher, year, edition, pages
2025. , p. 43
National Category
Mathematical sciences
Identifiers
URN: urn:nbn:se:hig:diva-47413OAI: oai:DiVA.org:hig-47413DiVA, id: diva2:1971612
Subject / course
Mathematics
Educational program
no programme (freestanding course)
Supervisors
Examiners
Available from: 2025-06-18 Created: 2025-06-17 Last updated: 2025-10-02Bibliographically approved

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