compute the arithmetic mean of the characters (bytes) in a string - Maple Help

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StringTools[IndexOfCoincidence] - compute the arithmetic mean of the characters (bytes) in a string

Calling Sequence

IndexOfCoincidence( s )

Parameters

s

-

Maple string

Description

• 

The IndexOfCoincidence(s) command returns the index of coincidence of a sample s of text. It can be defined by the formula addfchfch1,ch=Ι1..255nn1, where for each character ch, fch is the frequency with which ch occurs in the input string.

• 

The index of coincidence is returned as a floating point number, and the calculation is carried out at hardware precision.

• 

In elementary cryptanalysis, the index of coincidence is often used in conjunction with the Kasiski test to attempt to determine the number of alphabets used in a polyalphabetic substitution cipher.

Examples

withStringTools:

IndexOfCoincidencefoo

0.333333333333333315

(1)

IndexOfCoincidenceRandom100000

0.00392208322083220824

(2)

See Also

string, StringTools, StringTools[Kasiski]


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