Calculus of variationsSee also what's at Wikipedia, your library, or elsewhere.
Broader term:Narrower terms:Used for: Isoperimetrical problems
 Variations, Calculus of

Filed under: Calculus of variations
Filed under: Convex domains
Filed under: Convex bodiesFiled under: Functional analysis
Filed under: Approximation theory
Filed under: Extrapolation
Filed under: Gamma ray spectrometry
Filed under: Cosmic ray showersFiled under: Interpolation
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Filed under: Maximum entropy methodFiled under: Function spacesFiled under: Functor theoryFiled under: Operator theory Holomorphic Spaces (1998), ed. by Sheldon Jay Axler, John E. McCarthy, and Donald Sarason (PDF files with commentary at msri.org)
Filed under: Differential operators
Filed under: AtiyahSinger index theorem
Filed under: Elliptic operatorsFiled under: Spectral geometryFiled under: Linear operators
Filed under: Jacobi operatorsFiled under: Operator algebras Operator Algebras and Quantum Statistical Mechanics, by Ola Bratteli and Derek W. Robinson
Filed under: Noncommutative differential geometryFiled under: Spectral theory (Mathematics)
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Items below (if any) are from related and broader terms.
Filed under: Maxima and minima Lectures on the Theory of Maxima and Minima of Functions of Several Variables (Weierstrass' Theory) (University of Cincinnati bulletin #13; 1902), by Harris Hancock
Filed under: Mathematical optimization Optimization Algorithms on Matrix Manifolds (2008), by P.A. Absil, R. Mahony, and R. Sepulchre (PDF files with commentary at Princeton)
 Iterative Methods for Optimization (Philadelphia: Society for Industrial and Applied Mathematics, c1999), by C. T. Kelley (PDF at siam.org)
 Lecture Notes on Optimization (electronic edition of "Notes on Optimization", 1998), by Pravin Pratap Varaiya (PDF at Berkeley)
 The Design of Approximation Algorithms (electronic prepublication edition, c2011), by David P. Williamson and David Bernard Shmoys (PDF files with commentary at designofapproxalgs.com)
 Randomness and Optimal Estimation in Data Sampling (second edition, 2002), by Mohammad Khosnevisan, Housila P. Singh, S. Saxena, Sarjinder Singh, and Florentin Smarandache (PDF at UNM)
More items available under broader and related terms at left. 