C=compressor program like Zip
x and y are the 2 strings you want to compare
I works by simply compressing three things. The first text string C(x), the second C(y) and then the concatenation both strings together c(xy).
Apply the formula and you get a distance score between the 2 strings from 0 to 1 (plus a slight error amount). 0 means the articles are identical, and 1 means they are absolutely dissimilar.
NCD was discovered by Rudi Cilibrasi and Paul Vitanyi as described in thier 2005 paper "Clustering by Compression"
Consider the following article:
What If He Had Gone on Vacation-Jack Kilby describes how he developed the world's first integrated circuits.
"After several interviews, I was hired by Willis Adcock of Texas Instruments. My duties were not precisely defined, but it was understood that I would work in the general area of microminiaturization. Soon after starting at TI in May 1958, I realized that since the company made transistors, resistors, and capacitors, a repackaging effort might provide an effective alternative to the Micro-Module. I therefore designed an IF amplifier using components in a tubular format and built a prototype. We also performed a detailed cost analysis, which was completed just a few days before the plant shut down for a mass vacation.
"As a new employee, I had no vacation time coming and was left alone to ponder the results of the IF amplifier exercise. The cost analysis gave me my first insight into the cost structure of a semiconductor house. The numbers were high — very high — and I felt it likely that I would be assigned to work on a proposal for the Micro-Module program when vacation was over unless I came up with a good idea very quickly. In my discouraged mood, I began to feel that the only thing a semiconductor house could make in a cost-effective way was a semiconductor. Further thought led me to the conclusion that semiconductors were all that were really required — that resistors and capacitors, in particular, could be made from the same material as the active devices.
"I also realized that, since all of the components could be made of a single material, they could also be made in situ, interconnected to form a complete circuit. I then quickly sketched a proposed design for a flip-flop using these components. Resistors were provided by bulk effect in the silicon, and capacitors by p-n junctions.
"These sketches were quickly completed, and I showed them to Adcock upon his return from vacation. He was enthused but skeptical and asked for some proof that circuits made entirely of semiconductors would work. I therefore built up a circuit using discrete silicon elements. Packaged grown-junction transistors were used. Resistors were formed by cutting small bars of silicon and etching to value. Capacitors were cut from diffused silicon
power transistor wafers, metallized on both sides. This unit was assembled and demonstrated to Adcock on August 28, 1958.
"Although this test showed that circuits could be built with all semiconductor elements, it was not integrated. I immediately attempted to build an integrated structure as initially planned. I obtained several wafers, diffused and with contacts in place. By choosing the circuit, I was able to lay out two structures that would use the existing contacts on the wafers. The first circuit attempted was a phase-shift oscillator, a favorite demonstration vehicle for linear circuits at that time.
"On September 12, 1958, the first three oscillators of this type were completed. When power was applied, the first unit oscillated at about 1.3 megacycles.
"The concept was publicly announced at a press conference in New York on March 6, 1959. Mark Shepherd said, "I consider this to be the most significant development by Texas Instruments since we divulged the commercial availability of the silicon transistor." Pat Haggerty predicted the circuits first would be applied to the further miniaturization of electronic computers, missiles, and space vehicles and said that any
application to consumer goods such as radio and television receivers would be several years away."
television program in 1997 said about the integrated circuit and Jack Kilby, "One invention we can say is one of the most significant in history -- the microchip, which has made possible endless numbers of other inventions. For the past 40 years, Kilby has watched his invention change the world. Jack Kilby — one of the few people who can look around the globe and say to himself 'I changed how the world functions.'"
Can NCD work as a relationship classifier in news articles?
First, I ran a part of speech tagger on the article text and then looked-up all entities (proper nouns) in Wikipedia. The Wikipedia articles were then used to build a related word-list for each entity. Next I compute the normalized compression distance (NCD) pair-wise for each entity to get a distance matrix. Cluster the matrix and a nice binary graph appears using dot and the relationships begin to appear.
From the 50 entities mapped below, a few relations are apparent. (Probably should have just picked the top 25 entities though, because the clustering works better with fewer items.)
A) Mark Shepherd and Willis Adcock are related through Jack Kilby
B) The integrated circuit, transistor, capacitor and resistor are related by silicon.
C) Concepts and ideas are related through thought.