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neural networks algorithms applications and programming techniques phần 5

gây ra sự ức chế bên giữa các đơn vị trên mỗi cột. Đồng bằng sông đầu tiên đảm bảo rằng sự ức chế này được giới hạn trong mỗi cột, trong đó i = j. Vùng đồng bằng thứ hai đảm bảo rằng mỗi đơn vị không ức chế bản thân. Sự đóng góp của nhiệm kỳ thứ ba trong phương trình năng lượng có lẽ là không trực quan như vậy là lần đầu tiên hai. | 4.3 The Hopfield Memory 153 causes a lateral inhibition between units on each column. The first delta ensures that this inhibition is confined to each column where i j. The second delta ensures that each unit does not inhibit itself. The contribution of the third term in the energy equation is perhaps not so intuitive as the first two. Because it involves a sum of all of the outputs it has a rather global character unlike the first two terms which were localized to rows and columns. Thus we include a global inhibition C such that each unit in the network is inhibited by this constant amount. Finally recall that the last term in the energy function contains information about the distance traveled on the tour. The desire to minimize this term can be translated into connections between units that inhibit the selection of adjacent cities in proportion to the distance between those cities. Consider the term DdxY 6j i i 0j.i-i For a given column j i.e. for a given position on the tour the two delta terms ensure that inhibitory connections are made only to units on adjacent columns. Units on adjacent columns represent cities that might come either before or after the cities on column j. The factor -DdxY ensures that the units representing cities farther apart will receive the largest inhibitory signal. We can now define the entire connection matrix by adding the contributions of the previous four paragraphs Txi.Yj -AẻxY l-bij -BSij ỉ-ỗxY -C-Ddx Y bj.i 1 bj.i-i 4.30 The inhibitory connections between units are illustrated graphically in Figure 4.11. To find a solution to the TSP we must return to the equations that describe the time evolution of the network. Equation 4.24 is the one we want Here we have used N as the summation limit to avoid confusion with the n previously defined. Because all of the terms in Tij contain arbitrary constants and A can be adjusted to any desired values we can divide this equation by C and write du dt where r RC the system time constant and .