Senin, 23 April 2012

Indian Tale: The Story of Rice Grains on the Chessboard

About 1260 AD, Ibn Khallikan, a Kurdish historian living in the Abbasid Empire (modern Iraq, wrote an encyclopedia with biographies of many famous men (though no women). One of the biographies includes a story about chaturanga (which later known as chess) and the meaning of "exponential growth." The story takes place in India, because Ibn Khallikan knew that chess was a game that came from India.
According to this story, King Shihram was a tyrant who loved to play games. But he had gotten bored of the games that were present at the time and wanted a new game that was much more challenging. King Shihran like to oppressed his subjects. One of his subjects, a wise man, a poor mathematician named Sissa ibn Dahir. After months of struggling with all kinds of ideas the mathematician came up with the game of Chaturanga. The game had two armies each lead by a King who commanded the army to defeat the other by capturing the enemy King. It was played on a simple 8x8 square board. King Shihram was so pleased that he ordered that the game of chess should be preserved in the temples, and said that it was the best thing he knew of to train generals in the art of war, a glory to religion and the world, and the foundation of all justice.
Then King Shihram asked Sissa ben Dahir what reward he wanted. Sissa answered that he didn't want any reward, but the king insisted. Finally Sissa said that he would take this reward "I would like one grain of rice for the first square of the board, two grains for the second, four grains for the third and so on doubled for each of the 64 squares of the game board" said the mathematician. "Is that all?" asked the King, "Why don't you ask for gold or silver coins instead of rice grains". "The rice should be sufficient for me." replied the mathematician.
"What a dummy!" thought the king. "That's a tiny reward; I would have given him much more." He ordered his slaves to bring out the chessboard and they started putting on the rice. Everything went well for a while, but the king was surprised to see that by the time they got halfway through the chessboard the 32nd square required more than four billion grains of rice, or about 100,000 kilos of rice. Now Sissa didn't seem so stupid anymore. Even so, King Shihram was willing to pay up.
But as the slaves began on the second half of the chessboard, King Shihram gradually realized that he couldn't pay that much rice -. In fact the whole kingdoms supply of rice was exhausted before the 30th square was reached. "You have provided me with such a great game and yet I cannot fulfill your simple wish. You are indeed a genius." said the King and offered to make the mathematician his top most advisor instead.
To finish the chessboard you would need as much rice as six times the weight of all the living things on Earth.

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