Definite and Semidefinite Quadratic Forms Author(s): Gerard Debreu Source: Econometrica, Vol. 20, No. 2 (Apr., 1952), pp. 295-300 Published by: The Econometric Society Stable URL: http://www.jstor.org/stable/1907852 Accessed: 11-08-2015 16:59 UTC Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at http://www.jstor.org/page/ info/about/policies/terms.jsp JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact
[email protected]. The Econometric Society is collaborating with JSTOR to digitize, preserve and extend access to Econometrica. http://www.jstor.org This content downloaded from 73.24.179.250 on Tue, 11 Aug 2015 16:59:18 UTC All use subject to JSTOR Terms and Conditions DEFINITE AND SEMIDEFINITE QUADRATIC FORMS1 BY GERARD DEBREU THE PROBLEM of maximization (or minimization) of a function f(s) of a vector i, possibly constrained by m relations gj(t) = 0 (j = 1, , m), is outstanding in the classical economic theories of the consumer (who maximizes utility subject to a budgetary constraint) and of the firm (which maximizes profit subject to technological and other constraints). The calculus treatment of this question (see for example [5]) leads to a scrutiny of the conditions that a quadratic form be definite or semi- definite, with or without linear constraints.