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A Hopfield neural network is system used to replicate patterns of information that it has learned. It is modeled after the neural network found in the human brain, though it is created out of artificial components. First designed by John Hopfield in 1982, the Hopfield neural network can be used to discover patterns in input and can process complicated sets of instructions. It is also used in the study of human memory.
The Hopfield neural network is made out of a system of units that are connected to one another as a web in which every unit is connected to every other unit. Though the units are all connected to each other, an individual unit does not form a connection with itself. When he first created this model, Hopfield used the binary values 0 and 1 to describe the activity of each unit in the network. Though this system is still in use, many scientists now use -1 and +1 to describe the activity of the units. A unit in the neural network is said to be a 0 or -1 if its threshold has not yet been met and a 1 or +1 if its threshold has been met or exceeded.
The units in a Hopfield neural network are activated and release energy once their threshold has been met. When a certain input is given to a Hopfield neural network, it is able to echo that input back out through the series of complex connections between each of the units. Even in a system with only 4 individual units, there are 12 connections that information can be sent along. Complex networks can contain millions of connections, which makes it possible for them to echo long strings or patterns of binary code.
Before a Hopfield neural network is able to echo a pattern, it must first be taught the pattern it is looking for. Once a system knows a certain pattern, it will be able to echo it whenever it recognizes it again. This makes these networks useful for finding patterns in large amounts of data.
Though these networks are able to recognize patterns, they can recognize a pattern incorrectly, especially if the patterns are remembered in parts of the neural network that are close to one another. This same process occurs in human memory, which can be modeled through the use of the Hopfield neural network. Research into innacuracy in memory and in the strengthening of memory in humans can be done using Hopfield neural networks.