text: OK, the answer is very long winded, its been a while since I done some Eigen Vectors, but to help you to bring you upto speed look at the links.\n\nNow in terms of Engineering, these are very important to us and are used to find out stability problems, and solve mechanical systems. In terms of facial recognition, I think fuzzy logic is usually used if not AI, as for using Eigen Vectors, I'm not sure, I suspect that one would take an image of the face and then break it up into small pixels, i.e. place a grid on top of the face, then try pattern matching methods to find a match of the face, or try and find the ratios of distances between eyes and other fixed features.\n\nI'm sorry that its not much help, but its a very hard question, but check out the sites\n\nI hope that Helps\n\nAnhar Hussain Miah