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Multiplicative Persistence

Code style: black

pytest

For context, read the article on Medium.

Installation

With Python 3.7, run the following command:

pip install -r requirements.txt

Execute search

The command...

python cli.py --start 475 --end 476

...will expand the two MP cubes from the powers 475 to 476. Full CLI:

Usage: cli.py [OPTIONS]

Options:
  -s, --start INTEGER    What power should the MP search begin with?
                         [required]

  -e, --end INTEGER      What power should the MP search end with?  [required]
  -o, --output-dir TEXT  The directory where the output JSON be written
                         [default: output]

  --help                 Show this message and exit.

All Solutions

all_solutions.txt contains the dictionary output from our algorithm. The first column, in the form "x,x,x,x,x,x,x,x" tells us the number of twos, threes, fours, fives, and so on in a number. (We don’t track the number of ones because there could be any number.) The second column contains the number itself, and the third column are the factors in the form (x, x, x, x). This gives us the number in terms of its factors (2x, 3x, 5x, 7x).

For example, the number 117649 has one 4, one 7, one 6, and one 9 — so it is represented by 0,0,1,0,1,1,0,1. It's equal to 76 so it's represented by (0, 0, 0, 6).

The JSON

dict_f475.json contains all the information in the all_solutions.txt file above. The dictionary is formatted such that when constructing the MP tree, we search for the next highest node.

Say, for example, we are looking for a node upstream of 5. 5’s factors are 1 and 5, so we’d search for the key ‘0,0,0,1,0,0,0,0’, and we are returned the list [[5, (0, 0, 1, 0)], [15, (0, 1, 1, 0)]]. We’ve found the upstream node 15, which can be factored into (31)(51). We are now looking for an upstream node that contains one three and one five. By plugging ‘0,1,0,1,0,0,0,0’ into the dictionary, we get back [[35, (0, 0, 1, 1)], [315, (0, 2, 1, 1)], [135, (0, 3, 1, 0)]]. We would continue this process until we reach a dead end.

Visualizing MP Trees

The visualize_tree folder contains functions that transform our main dictionary into a nested json that can be used in a D3 tree object, as shown in the Medium article.

Install black pre-commit

In order to follow black style guidelines, simply run the following command:

pre-commit install

This will prevent you from committing un-styled code.