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clean up
#REDIRECT [[Recursion]]
'''Recursion''' is the repeated application of a procedure or definition through reference to itself.
==In Mathematics==
There's a simple procedure for finding out whether a number is divisible by three.
#If the number is 3, 6, or 9 then it's divisible by three.
#Otherwise, add all the digits of the number; if the sum of the digits is divisible by three, then so is the original number.
Examples:
* 12 => 1 + 2 = 3 (yes)
* 14 => 1 + 4 = 5 (no)
* 96 => 9 + 6 = 15; 15 => 1 + 5 = 6
==In Computing==
Recursion is a technique whereby a [[function]], in order to accomplish a task, calls itself to accomplish part of the task.
Every recursive solution involves two major parts or cases, the second part having three components:
* base case(s), in which the problem is simple enough to be solved directly, and
* recursive case(s). A recursive case has three components:
::1. divide the problem into one or more simpler or smaller parts of the problem,
::2. call the function (recursively) on each part, and
::3. combine the solutions of the parts into a solution for the problem.
These exercises are useful to see examples of recursion:
:1. Write a function to compute the sum of all numbers from 1 to n.
:2. Write a function to compute 2 to the power of a non-negative integer.
:3. Write a function to compute any number to the power of a non-negative integer.
==External links==
* [http://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-00sc-introduction-to-computer-science-and-programming-spring-2011/unit-1/lecture-6-recursion/ Unit on recursion in free online computer science course from MIT.]
[[Category:Computer Science]]
[[Category:Mathematics]]