In an Old Notebook (Generating Random Sequences VI)

April 4, 2017

Looking for something else in old notebooks, I found a diagram with no other indication, but clearly a low-cost random generator.

So, why not test it?

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Ad Hoc Compression Methods: Digram Coding

February 17, 2009

Ad hoc compression algorithms always sound somewhat flimsy, but they still have their usefulness whenever the data you have to compress exhibits very special properties or is extremely short. Universal compression algorithms need a somewhat lengthy input to adapt sufficiently to yield good compression. Moreover, you may not have the computing power (CPU speed, RAM and program space) to implement full-blown compressors. In this case also, an ad hoc algorithm may be useful.

Digram (bigram, digraph, bigraph) coding is one of those ad hoc algorithms. Digram coding will compress text (or any source, really) by finding pairs of symbols that appear often and assigning them codes corresponding to used symbols, if any.


Let us see in detail what digram compression is, and how effective it really is.

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