logarithmic growth

{{short description|Growth at a rate that is a logarithmic function}}

Image:Log.svg

In mathematics, logarithmic growth describes a phenomenon whose size or cost can be described as a logarithm function of some input. e.g. y = C log (x). Any logarithm base can be used, since one can be converted to another by multiplying by a fixed constant.{{citation|title=Programming With C++ And Data Structures, 1E|first=G.|last=Litvin|publisher=Vikas Publishing House Pvt Ltd|year=2009|isbn=9788125915454|pages=AAL-9 – AAL-10|url=https://books.google.com/books?id=A-uXzNVR9oAC&pg=PT479}}. Logarithmic growth is the inverse of exponential growth and is very slow.{{citation|title=Calculus|first=Denise|last=Szecsei|publisher=Career Press|year=2006|isbn=9781564149145|pages=57–58|url=https://books.google.com/books?id=a95EDwAAQBAJ&pg=PT58}}.

A familiar example of logarithmic growth is a number, N, in positional notation, which grows as log_b (N), where b is the base of the number system used, e.g. 10 for decimal arithmetic.{{citation|title=Data Compression: The Complete Reference|first1=David|last1=Salomon|first2=G.|last2=Motta|first3=D.|last3=Bryant|publisher=Springer|year=2007|isbn=9781846286032|page=49|url=https://books.google.com/books?id=ujnQogzx_2EC&pg=PA49}}. In more advanced mathematics, the partial sums of the harmonic series

:$1+\backslash frac\{1\}\{2\}+\backslash frac\{1\}\{3\}+\backslash frac\{1\}\{4\}+\backslash frac\{1\}\{5\}+\backslash cdots$

grow logarithmically.{{citation|title=Mathematical Mysteries: The Beauty and Magic of Numbers|first=Calvin C.|last=Clawson|publisher=Da Capo Press|year=1999|isbn=9780738202594|page=112|url=https://books.google.com/books?id=cqz13UpQSuMC&pg=PA112}}. In the design of computer algorithms, logarithmic growth, and related variants, such as log-linear, or linearithmic, growth are very desirable indications of efficiency, and occur in the time complexity analysis of algorithms such as binary search.

Logarithmic growth can lead to apparent paradoxes, as in the martingale roulette system, where the potential winnings before bankruptcy grow as the logarithm of the gambler's bankroll.{{citation|title=Understanding Probability|first=Henk|last=Tijms|publisher=Cambridge University Press|year=2012|isbn=9781107658561|page=94|url=https://books.google.com/books?id=FjpRJJ65HwIC&pg=PA94}}. It also plays a role in the St. Petersburg paradox.{{citation|title=Utility-Based Learning from Data|first1=Craig|last1=Friedman|first2=Sven|last2=Sandow|publisher=CRC Press|year=2010|isbn=9781420011289|page=97|url=https://books.google.com/books?id=mPU12DwrVxsC&pg=PA97}}.

In microbiology, the rapidly growing exponential growth phase of a cell culture is sometimes called logarithmic growth. During this bacterial growth phase, the number of new cells appearing is proportional to the population. This terminological confusion between logarithmic growth and exponential growth may be explained by the fact that exponential growth curves may be straightened by plotting them using a logarithmic scale for the growth axis.{{citation|title=More Fallacies, Flaws & Flimflam|first=Edward J.|last=Barbeau|authorlink=Edward Barbeau|publisher=Mathematical Association of America|year=2013|isbn=9780883855805|page=52|url=https://books.google.com/books?id=seRaAQAAQBAJ&pg=PA52}}.