Positional Mimic Cipher (PM-Cipher)

[quimqu]

On a more detailed note, keep in mind that the second order entropy (either the unconditional or the conditioal one) is a single value representing a 2-dimensional matrix of probability values.
There are infinitely many different such matrices (probability distributions) that all lead to the same entropy.

To get a really good match, one should be able to approach the entire distribution.
Note, that this would be a major achievement, and a sign that one is potentially onto something.

(Of course, a Naibbe-type cipher, that recomposes the text from known segments of it, may be able to mimick it quite well due to its very nature.)

Hi René,

Following your point about second-order entropy being just a single scalar, I’ve been comparing full bigram distributions directly. For each text I build the 2D bigram probability matrix (word-reset, normalized), flatten it, and compute the Jensen–Shannon divergence (JSD) against the Voynich matrix. (For those who don't know about it, JSD is 0 when two distributions are identical and approaches 1 as they diverge; it’s not a “percent similarity,” but it’s a clean, symmetric way to quantify how close the entire matrix is). I also plot the corresponding heatmaps so the structure of transitions is visible rather than compressed into one number.

Here is a table with the results:

Text	JSD
Vietnamese with special chars	0.504
Vietnamese without special chars	0.362
Romeo and Juliet	0.299
De docta Ignorantia	0.331
In Psalmum David CXVIII Expositio	0.316
Lazarillo de Tormes	0.340
Triant lo Blanch	0.317

My optimization work tries to minimize JSD while steering H₂ toward the Voynich’s level (≈2.1). The goal is not just to match a single entropy value but to approach the full bigram distribution. I’m attaching some heatmaps of the lowest JSD cases and Voynich so you can see the contrasts.











It is obvious that I need to find a better suit of text, in terms of language and writting (a scientific text may have better JSD than a romance text in the same language).

If you think it is of interest and anyone want to check any other text, please let me know. I am aware that old slave languages may have good patterns, but I have no text. I could make a loop to check different texts. If they can come in lower and in a single string with a dot between the words, that would be perfect. If not, it will take me longer...