Recursion

Recursion

the process of defining something with iteself as the definition

This is a bit tough to grasp, but it is like defining a word with the word in it.
Here is an example of a recursive definition. A class is A) a student or B) a student and another class.
See with this definition you can have another amount of students in a class. You can have a studnet and a class, but a class can be a student, and another class, etc.

Recursive Function

a function defined recursively by making a call to iteself

This is the use of recursion. Some function can be defined more easily recursively. This can be easily seen with searching, sorting functions, and data strucures.
Recursive functions are called in a stack. The function makes a call to itself many times, but will evaluate the calls backwards when the last one is called. See the example code.
It is better to return values directly than hold variables for them since more memory is taken up.
Recursive functions can easily be defined iteratively, and they are often tail end recursive.

Delimiter

the condition that haults recursive calls of a function

Tail End Recursion

recursion has only lines of code created in the calls

Another tricky concept of recursion better seen in code.
In general tail end recursion is better than non tail end, since compilers translate them iteratively, which has less memory overhang.

Divide and Conquer

recursion in which the calls are spreading to multiple calls

Maze Searching

a problem in which a person has to find the exit of a maze which is easily solved with recursion

Fractals

a picture defined recursively

These are pictures often when you you take a close up then they look the same. Think of a picture within a picture within a picture...
Fractals often a used to simulate natural terrains.

Towers of Hanoi

a common recursive example

Let me elaborate, ahem... One day some monks at Hanoi asked God when the world will end. Then God gave them a puzzle. It was three poles with 64 concentric disks on one pole. The monks were to move all the disks to the oposite pole, with only moving one disk at a time, and never having a larger disk on a smaller one. When the puzzle is solved then the world will end. Don't worry. Moving one disk to a pole in one second, it will take about a few million years to completely solved.
Now this puzzle can easily be solved recursivly. You just move N disks to the middle pole. Move the Nth disk to the third pole, then move all the other disks to the third pole. Simple.