Reply To: Typo in Madness’ “A book on classical cryptography”?
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Hey @madness (hopefully you still see this although the cipher challenge isn’t currently active)
Going through your book now – currently on Unit 9 (Tetragram Frequency), but I’m a bit stumped, and I wondered if you could explain what you meant here in a bit more detail?
I half-understood this equation [F= ∑_tetragrams f log f_English], but I don’t understand this sentence at all:
“Note that to calculate this, we do not have to find the frequencies of every tetragram in the piece of text; instead, we merely perform the sum over the text with a one in place of f and later divide by the number of terms in the sum. ”
I thought that the equation meant you ARE in fact going through every single occuring tetragram (e.g. XXXX) in a piece of text, and adding together the number of times XXXX occurs by the logarithm of the corresponding XXXX counts taken from my corpus
Could you provide a further breakdown of what to do?
(PS. Your book is a godsend)