Advances in Computational Mathematics

, Volume 43, Issue 6, pp 1261–1282 | Cite as

Solving F(z + 1) = b F(z) in the complex plane

  • William PaulsenEmail author
  • Samuel Cowgill


The generalized tetration, defined by the equation F(z+1) = b F(z) in the complex plane with F(0) = 1, is considered for any b > e 1/e . By comparing other solutions to Kneser’s solution, natural conditions are found which force Kneser’s solution to be the unique solution to the equation. This answers a conjecture posed by Trappmann and Kouznetsov. Also, a new iteration method is developed which numerically approximates the function F(z) with an error of less than 10−50 for most bases b, using only 180 nodes, with each iteration gaining one or two places of accuracy. This method can be applied to other problems involving the Abel equation.


Tetration Abel’s functional equation Iteration Cross-track method 

Mathematics Subject Classification (2010)

26A18 30D05 39B12 


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© Springer Science+Business Media New York 2017

Authors and Affiliations

  1. 1.Arkansas State UniversityArkansasUSA

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