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chap0 - Chapter 0 Prologue Look around you Computers and...

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Chapter 0 Prologue Look around you. Computers and networks are everywhere, enabling an intricate web of com- plex human activities: education, commerce, entertainment, research, manufacturing, health management, human communication, even war. Of the two main technological underpinnings of this amazing proliferation, one is obvious: the breathtaking pace with which advances in microelectronics and chip design have been bringing us faster and faster hardware. This book tells the story of the other intellectual enterprise that is crucially fueling the computer revolution: efficient algorithms. It is a fascinating story. Gather ’round and listen close. 0.1 Books and algorithms Two ideas changed the world. In 1448 in the German city of Mainz a goldsmith named Jo- hann Gutenberg discovered a way to print books by putting together movable metallic pieces. Literacy spread, the Dark Ages ended, the human intellect was liberated, science and tech- nology triumphed, the Industrial Revolution happened. Many historians say we owe all this to typography. Imagine a world in which only an elite could read these lines! But others insist that the key development was not typography, but algorithms. Today we are so used to writing numbers in decimal, that it is easy to forget that Guten- berg would write the number 1448 as MCDXLVIII. How do you add two Roman numerals? What is MCDXLVIII + DCCCXII? (And just try to think about multiplying them.) Even a clever man like Gutenberg probably only knew how to add and subtract small numbers using his fingers; for anything more complicated he had to consult an abacus specialist. The decimal system, invented in India around AD 600, was a revolution in quantitative reasoning: using only 10 symbols, even very large numbers could be written down compactly, and arithmetic could be done efficiently on them by following elementary steps. Nonetheless these ideas took a long time to spread, hindered by traditional barriers of language, distance, and ignorance. The most influential medium of transmission turned out to be a textbook, written in Arabic in the ninth century by a man who lived in Baghdad. Al Khwarizmi laid out the basic methods for adding, multiplying, and dividing numbers—even extracting square roots and calculating digits of π . These procedures were precise, unambiguous, mechanical, 11
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12 Algorithms efficient, correct—in short, they were algorithms , a term coined to honor the wise man after the decimal system was finally adopted in Europe, many centuries later. Since then, this decimal positional system and its numerical algorithms have played an enormous role in Western civilization. They enabled science and technology; they acceler- ated industry and commerce. And when, much later, the computer was finally designed, it explicitly embodied the positional system in its bits and words and arithmetic unit. Scien- tists everywhere then got busy developing more and more complex algorithms for all kinds of problems and inventing novel applications—ultimately changing the world.
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