(algorithm)

**Definition:**
A function of two parameters whose value grows very, very slowly.

**Formal Definition:** α(m,n) = min{i≥ 1: A(i, ⌊ m/n⌋) > log_{2} n} where A(i,j) is *Ackermann's function*.

**Also known as** α.

**See also**
*Ackermann's function*.

*Note:
This is not strictly the inverse of Ackermann's function. Rather, this grows as slowly as Ackermann's function grows quickly. *

* After [CLR90, page 452].*

Author: PEB

Go to the Dictionary of Algorithms and Data Structures home page.

If you have suggestions, corrections, or comments, please get in touch with Paul Black.

Entry modified 17 December 2004.

HTML page formatted Tue Feb 12 10:57:43 2019.

Cite this as:

Paul E. Black, "inverse Ackermann function", in
*Dictionary of Algorithms and Data Structures* [online], Vreda Pieterse and Paul E. Black, eds. 17 December 2004. (accessed TODAY)
Available from: https://www.nist.gov/dads/HTML/inverseAckermann.html