Idempotent

3 definitions found

From WordNet (r) 2.0 [wn]:

  idempotent
       adj : unchanged in value following multiplication by itself; "this
             matrix is idempotent"

From Jargon File (4.3.1, 29 Jun 2001) [jargon]:



  idempotent adj. [from mathematical techspeak] Acting as if used only
     once, even if used multiple times. This term is often used with respect
     to {C} header files, which contain common definitions and declarations
     to be included by several source files. If a header file is ever
     included twice during the same compilation (perhaps due to nested
     #include files), compilation errors can result unless the header file
     has protected itself against multiple inclusion; a header file so
     protected is said to be idempotent. The term can also be used to
     describe an initialization subroutine that is arranged to perform some
     critical action exactly once, even if the routine is called several
     times.
  
  

From The Free On-line Dictionary of Computing (27 SEP 03) [foldoc]:

  idempotent
       
          1. A function f : D -> D is idempotent if
       
          	f (f x) = f x  for all x in D.
       
          I.e. repeated applications have the same effect as one.  This
          can be extended to functions of more than one argument,
          e.g. Boolean & has x & x = x.  Any value in the {image} of an
          idempotent function is a {fixed point} of the function.
       
          2. This term can be used to describe {C} header files, which
          contain common definitions and declarations to be included by
          several source files.  If a header file is ever included twice
          during the same compilation (perhaps due to nested #include
          files), compilation errors can result unless the header file
          has protected itself against multiple inclusion; a header file
          so protected is said to be idempotent.
       
          3. The term can also be used to describe an initialisation
          subroutine that is arranged to perform some critical action
          exactly once, even if the routine is called several times.
       
          [{Jargon File}]
       
          (1995-01-11)