hamming

9n-Dimensional spaceWhen I became a professor, after 30 years of active research at Bell Telephone Laboratories, mainly in theMathematics Research Department, I recalled professors are supposed to think and digest past experiences.So I put my feet up on the desk and began to consider my past. In the early years I had been mainly incomputing so naturally I was involved in many large projects which required computing. Thinking abouthow things worked out on several of the large engineering systems I was partially involved in, I began, nowI had some distance from them, to see they had some common elements. Slowly I began to realize thedesign problems all took place in a space of n-dimensions, where n is the number of independentparameters. Yes, we build three dimensional objects, but their design is in a high dimensional space, 1dimension for each design parameter.I also need high dimensional spaces so later proofs will become intuitively obvious to you without fillingin the details rigorously Hence we will discuss n-dimensional space now.You think you live in three dimensions, but in many respects you live in a two dimensional space. Forexample, in the random walk of life, if you meet a person you then have a reasonable chance of meetingthat person again. But in a world of three dimensions you do not! Consider the fish in the sea whopotentially live in three dimensions. They go along the surface, or on the bottom, reducing things to twodimensions, or they go in schools, or they assemble at one place at the same time, such as a river mouth, abeach, the Sargasso sea, etc. They cannot expect to find a mate if they wander the open ocean in threedimensions. Again, if you want airplanes to hit each other, you assemble them near an airport, put them intwo dimensional levels of flight, or send them in a group; truly random flight would have fewer accidentsthan we now have!n-dimensional space is a mathematical construct which we must investigate if we are to understand whathappens to us when we wander there during a design problem. In two dimensions we have Pythagoras’theorem for a right triangle the square of the hypotenuse equals the sum of the squares of the other twosides. In three dimensions we ask for the length of the diagonal of a rectangular block, Figure 9.I. To find itwe first draw a diagonal on one face, apply Pythagoras’ theorem, and then take it as one side with the otherside the third dimension, which is at right angles, and again from the Pythagorean theorem we get thesquare of the diagonal is the sum of the squares of the three perpendicular sides. It is obvious from thisproof, and the necessary symmetry of the formula, as you go to higher and higher dimensions you will stillhave the square of the diagonal as the sum of the squares of the individual mutually perpendicular sideswhere the x i are the lengths of the sides of the rectangular block in n-dimensions.