Dini derivative

In mathematics and, specifically, real analysis, the Dini derivatives (or Dini derivates) are a class of generalizations of the derivative. They were introduced by Ulisse Dini.

The upper Dini derivative, which is also called an upper right-hand derivative,[1] of a continuous function

is denoted by and defined by

where is the supremum limit and the limit is a one-sided limit. The lower Dini derivative, , is defined by

where is the infimum limit.

If is defined on a vector space, then the upper Dini derivative at in the direction is defined by

If is locally Lipschitz, then is finite. If is differentiable at , then the Dini derivative at is the usual derivative at .

Remarks

and

See also

References

In-line references
  1. 1 2 Khalil, H.K. (2002). Nonlinear Systems (3rd ed.). Upper Saddle River, NJ: Prentice Hall. ISBN 0-13-067389-7.
General references
  • Lukashenko, T.P. (2001), "Dini derivative", in Hazewinkel, Michiel, Encyclopedia of Mathematics, Springer, ISBN 978-1-55608-010-4 .
  • Royden, H.L. (1968). Real analysis (2nd ed.). MacMillan. ISBN 978-0-02-404150-0. 
  • Brian S. Thomson; Judith B. Bruckner; Andrew M. Bruckner (2008). Elementary Real Analysis. ClassicalRealAnalysis.com [first edition published by Prentice Hall in 2001]. pp. 301–302. ISBN 978-1-4348-4161-2. 

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