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Concavifying the Quasiconcave

Author

Listed:
  • Christopher Connell

    (Department of Mathematics, Indiana University)

  • Eric Rasmusen

    (Department of Business Economics and Public Policy, Indiana University Kelley School of Business)

Abstract

We show that if and only if a real-valued function f is strictly quasiconcave except possibly for a at interval at its maximum, and furthermore belongs to an explicitly determined regularity class, does there exist a strictly monotonically increasing function g such that g o f is strictly concave. Moreover, if and only if the function f is either weakly or strongly quasiconcave there exists an arbitrarily close approximation h to f and a monotonically increasing function g such that g o h is strictly concave. We prove this sharp characterization of quasiconcavity for continuous but possibly nondifferentiable functions whose domain is any Euclidean space or even any arbitrary geodesic metric space. While the necessity that f belong to the special regularity class is the most surprising and subtle feature of our results, it can also be difficult to verify. Therefore, we also establish a simpler sufficient condition for concaviability on Euclidean spaces and other Riemannian manifolds, which suffice for most applications.

Suggested Citation

  • Christopher Connell & Eric Rasmusen, 2012. "Concavifying the Quasiconcave," Working Papers 2012-10, Indiana University, Kelley School of Business, Department of Business Economics and Public Policy.
  • Handle: RePEc:iuk:wpaper:2012-10
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    File URL: http://kelley.iu.edu/riharbau/RePEc/iuk/wpaper/bepp2012-10-connell-rasmusen.pdf
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    References listed on IDEAS

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    1. Matzkin, Rosa L. & Richter, Marcel K., 1991. "Testing strictly concave rationality," Journal of Economic Theory, Elsevier, vol. 53(2), pages 287-303, April.
    2. Richter, Marcel K. & Wong, K.-C.Kam-Chau, 2004. "Concave utility on finite sets," Journal of Economic Theory, Elsevier, vol. 115(2), pages 341-357, April.
    3. Aumann, Robert J, 1975. "Values of Markets with a Continuum of Traders," Econometrica, Econometric Society, vol. 43(4), pages 611-646, July.
    4. Mas-Colell, Andreu & Whinston, Michael D. & Green, Jerry R., 1995. "Microeconomic Theory," OUP Catalogue, Oxford University Press, number 9780195102680.
    5. Kannai, Yakar, 1977. "Concavifiability and constructions of concave utility functions," Journal of Mathematical Economics, Elsevier, vol. 4(1), pages 1-56, March.
    6. Yakar Kannai, 2005. "Remarks concerning concave utility functions on finite sets," Economic Theory, Springer;Society for the Advancement of Economic Theory (SAET), vol. 26(2), pages 333-344, August.
    7. Ginsberg, William, 1973. "Concavity and quasiconcavity in economics," Journal of Economic Theory, Elsevier, vol. 6(6), pages 596-605, December.
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    Cited by:

    1. Emmanuel Farhi & Iván Werning, 2013. "Estate Taxation with Altruism Heterogeneity," American Economic Review, American Economic Association, vol. 103(3), pages 489-495, May.

    More about this item

    Keywords

    quasiconcavity; quasiconvexity; concavity; convexity; unique maximum; maximization;

    JEL classification:

    • C02 - Mathematical and Quantitative Methods - - General - - - Mathematical Economics

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