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800 years since the publication of Liber Abaci, the book that introduced the decimal system and numbers to the West

It was first of all a revolution in the world of commerce

By Keith Devlin, Guardian

Fibonacci. The Roman system of indicating numbers was not suitable for complicated calculation operations

2002 marked the 800th anniversary of the publication of "Liber Abaci", the book that gave the numbers to the Western world. And yet, despite the efforts of many researchers, very little is known about the man who wrote it: Leonardo of Pisa, better known as Fibonacci.

Numbers are so common in the modern world that it is hard not to see them as a self-evident phenomenon; It is hard to see how essential they are. But it wasn't always like that. In fact, the way numbers are pronounced nowadays, using only 10 symbols, and the methods used for calculation - are less than 2,000 years old, and during most of that time the numbers as we know them today were not known in the Western world.

Before the advent of the modern method of writing numbers, the most common method was the one invented by the Romans. The Roman numeral system, which is still used in certain circumstances, is suitable for indicating numbers and performing simple addition and subtraction operations, but it is difficult to use for multiplication and division, and it cannot form a basis for scientific or technical research. In the Middle Ages merchants used an abacus to make calculations.

Then, in 1202, the young scholar Leonardo wrote the "Liber Abachi" (Book of Calculations), in which he described a new and particularly efficient method for writing numbers and performing calculations, which he learned from Arab scholars while traveling in North Africa. They themselves learned it from the Indians, who developed it over hundreds of years at the beginning of the first millennium.

As a young man, Fibonacci joined his father, who served as an Italian customs representative in the North African port city of Bugia (now part of Algeria). He noticed that the Arab scholars use an unusual method for writing numbers and performing calculations. Although the local merchants did not use the new method, Leonardo immediately realized that it could revolutionize the world of commerce. He wrote "Liber Abachi" shortly after returning to Pisa, in 1202. He did not target the book for scholars but for traders, and devoted efforts to explaining the concepts in a way that would enhance their practical world, while presenting many examples from everyday trading life.

Liber Abaci was not the first book written in Europe about the new numerical system, but because it was intended for traders, Fibonacci promised that it would become the most influential. This can be compared to the way in which "Windows" became the most common operating system for home computers, even though it appeared after Apple's Macintosh, which it imitated.

Leonardo opened the book with a detailed description of the Indo-Arabic numerals and the decimal system, in which the position of a digit in relation to other digits in a number determines its value. Fibonacci wrote detailed instructions explaining how to perform calculations using this method. He went on to present an extensive collection of problems designed to practice the new number system. Many of the problems were of a practical nature: problems concerning the prices of goods, calculation of profits and conversions between different currency rates. Others were more similar to the verbal problems that appear in modern algebra books, including the famous rabbit problem that led to the series of numbers now named after him - the Fibonacci sequence.

This series, starting with the numbers 34, 21, 13, 8, 5, 3, 2, 1, 1, is created by adding the last two numbers to create the next number in the series. It seems that Fibonacci did not study these numbers at all, but today we know that the Fibonacci series is found everywhere in nature: in the spiral patterns at the base of pineapples and acorns, in many inflorescences such as that of the sunflower, in the number of petals and leaves of flowers and plants, and on shells of sea ​​snails Some stock traders even claim that they can use the series to predict stock market movements.

The life and numbers of Fibonacci on the website

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