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MathGroup Archive 1998

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String patterns

Programming challenge:

Is there an elegant means of doing cryptanalysis in Mathematica as
opposed to any other language.  I am mainly thinking of
pattern-matching functions.  In this case, the pattern would be
dynamic, not predefined.  I am not certain how to create and test
patterns on the fly.

The primary task is to count letter, digraph, trigraph, and higher-order

Output for the trigraph case might look like this:

THE    0.01350000
AND    0.00709421
ION    0.00559429
ING    0.00510783
TIO    0.00466191
ENT    0.00458083
RES    0.00417545
BEP    0.00004054

The real number represents the fractional occurrence of the trigraph
among all trigraphs in the sample.  These were computed by a DOS
utility on a particular sample text.  The word "the" occurred 333 times
out of 24668 total trigraph sequences, giving an estimated probability
for this trigraph of 333/24668=0.01350000.

Trigraphs overlap.  If I parse the following phrase,

     "I love Mathematica"

then the first trigraph is "I l" (spaces count), the second is " lo",
and the third is "lov".

One must define an "alphabet" with a sorting order.  A good way to do
this is with a string variable like this:


How good is Mathematica at this kind of string manipultion and

Mark Evans

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