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Dirichlet, Peter Gustav Lejeune (1805–1859)

Peter Dirichlet
German mathematician who made significant contributions to number theory, analysis, and mechanics, and who is credited with the modern formal definition of a function. He taught at the universities of Breslau (1827) and Berlin (1828–1855) and in 1855 succeeded Carl Gauss at the University of Göttingen but died of a heart attack only three years later. Dirichlet continued Gauss's great work on number theory, publishing on Diophantine equations of the form x5 + y5 = kz5. His book Lectures on Number Theory (1863) is similar in stature to Gauss's earlier Disquisitiones and founded modern algebraic number theory. In 1829 he gave the conditions sufficient for a Fourier series to converge (though the conditions necessary for it to converge are still undiscovered).

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