@TechReport{Langdon97,
  author      = "William B Langdon",
  title       = {Fitness Causes Bloat: Simulated Annealing, Hill Climbing and Populations},
  institution = {University of Birmingham, School of Computer Science},
  number      = {CSRP-97-22},
  month       = {September},
  year        = {1997},
  email       = {W.B.Langdon@cs.bham.ac.uk},
  file        = {/1997/CSRP-97-22.ps.gz},
  url         = {ftp://ftp.cs.bham.ac.uk/pub/tech-reports/1997/CSRP-97-22.ps.gz},
  abstract    = {In many cases programs length's increase (known as
                 ``bloat'', ``fluff'' and increasing ``structural
                 complexity'') during artificial evolution. We show bloat
                 is not specific to genetic programming and suggest it is
                 inherent in search techniques with discrete variable
                 length representations using simple static evaluation
                 functions. We investigate the bloating characteristics of
                 three non-population and one population based search
                 techniques using a novel mutation operator.
                 
                 An artificial ant following the Santa Fe trail problem is
                 solved by simulated annealing, hill climbing, strict hill
                 climbing and population based search using two variants of
                 the the new subtree based mutation operator. As predicted
                 bloat is observed when using unbiased mutation and is
                 absent in simulated annealing and both hill climbers when
                 using the length neutral mutation however bloat occurs
                 with both mutations when using a population.
                 
                 We conclude that there are two causes of bloat.
                 },
}