Approximately Convex Functions

  • Donald H. Hyers
  • George Isac
  • Themistocles M. Rassias
Part of the Progress in Nonlinear Differential Equations and Their Applications book series (PNLDE, volume 34)


So far we have discussed the stability of various functional equations. In the present section, we consider the stability of a well-known functional inequality, namely the inequality defining convex functions:
$$f\left( {\lambda x + \left( {1 - \lambda } \right)y} \right) \leqslant \lambda f\left( x \right) + \left( {1 - \lambda } \right)f\left( y \right),$$
where\(0 \leqslant \lambda \leqslant 1\), with x and y in R n , A function f : S→R, where S is a convex subset of R n , will be called ε-convex (where ε > 0) if the inequality:
$$f\left( {\lambda x + \left( {1 - \lambda } \right)y} \right) \leqslant \lambda f\left( x \right) + \left( {1 - \lambda } \right)f\left( y \right) + \varepsilon $$
holds for all \(\lambda\)in [0, 1] and all x, y in S.


Functional Equation Convex Function Convex Subset Interior Point Topological Vector Space 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


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Copyright information

© Springer Science+Business Media New York 1998

Authors and Affiliations

  • Donald H. Hyers
  • George Isac
    • 1
  • Themistocles M. Rassias
    • 2
  1. 1.Department of Mathematics and Computer ScienceRoyal Military College of CanadaKingstonCanada
  2. 2.Department of MathematicsNational Technical University of AthensAthensGreece

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