In a special Feb. 2 , 2016, ground hog day blog post, I announced the first large release by our company, artiste-qb.net, of Pythonic open-source Quantum Fog. As you may or may not know, Quantum Fog was originally (almost 20 years ago) a Mac-only application written in C++. The GitHub page for Quantum Fog contains the legacy C++ code of yee ole Quantum Fog, plus the shining new Python code which will attempt to reproduce all the functionality of the old application plus much more. So are we there yet, you ask. Not quite, but making steady progress.
These are some of the things the new QFog can do so far:
- It can do inference with evidence using 3 methods: Join Tree, MCMC (Monte Carlo) and brute force (enumeration of all Feynman paths).
- It can do inference by those 3 methods for BOTH, quantum Bayesian networks (QBnets) and classical Bayesian networks (CBnets).
- It can read and write CBnets and QBnets in two formats .dot and .bif (bif stands for Bayesian Interchange Format).
- It can draw the CBnet and QBnet graphs using only matplotlib and networkx, included in the usual Python installation. This is fine for most purposes, but if you want a super high quality plot of your graph, you should use the .dot file that Quantum Fog generates and fine-tune that with GraphViz.
QFog integrates CBnets and QBnets seamlessly. You can use all subroutines for either classical or quantum analysis simply by changing a Boolean input parameter called
- .dot and .bif files are both just .txt files. The .dot format is used by a really wonderful, free software called GraphViz. There are several very helpful Bayesian network repositories that store Bnets in the .bif format. The .dot and .bif formats are complementary. The .dot format is good for storing visual layout info, not good for storing the numerical tables associated with each node. The .bif format is good in the opposite way.
- The “join tree” (or junction tree, or clique tree or belief) propagation method is an exact method (Other methods, like MCMC, are approximate). The Join Tree method caused a mini revolution in the Bayesian networks field starting from 1990 or so. Before then, people had been discouraged by a proof that calculating probabilities from a Bnet by brute force is NP hard. But the Join Tree method takes advantage of the graph structure. If I understand it correctly, its complexity is exp(k) whereas brute force is exp(n), where n is the total number of nodes and k is the number of nodes in the fattest clique (k is called the width of the join tree). The Join Tree algorithm still has exponential complexity, but is much better than the brute force algo. The join tree algo used by the new Qfog is the one described in the following very detailed and clear, cookbook paper:
Inference in Belief Networks, A Procedural Guide, by C. Huang and A. Darwiche (1996)
I end by waxing poetic in a nerdy way. Here are 3 things that remind me of quantum fog:
Fog Machines, very cool. An essential prop in the shooting of moody films, in rock concerts, in serious Halloween home decorations and in nerd experiments. They work by either (1) pushing a mixture of water and (glycol or glycerin or mineral oil) over a heated surface, or (2) dropping dry ice, i.e., solid CO2, into water heated near boiling point. Some use solid N2 or O2 instead to get a different kind of fog.
Aerogels, very cool too.
They are very good thermal insulators. You can put your hand on one side and a Bunsen Burner flame on the other side of a ½ inch thick layer of aerogel and not feel the heat.
The ones that are almost transparent and ethereal looking are the silica aerogels. They are kind of expensive though, like $50 for a 1 x 1 x 0.5 in. specimen.
“Aerogel was first created by Samuel Stephens Kistler in 1931, as a result of a bet with Charles Learned over who could replace the liquid in “jellies” with gas without causing shrinkage.”
“The first aerogels were produced from silica gels. Kistler’s later work involved aerogels based on alumina, chromia and tin dioxide. Carbon aerogels were first developed in the late 1980s.”
And of course, the Golden Gate Bridge shrouded in fog.