File Name: neural network architectures and learning algorithms .zip
Sign in. The zoo of neural network types grows exponentially.
- Artificial Neural Networks
- Artificial neural network
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- Neural networks
They are inspired by the neurological structure of the human brain.
Review in "Computer Reviews". Reported errata. The biological paradigm PDF. Threshold logic PDF. Perceptron learning PDF.
Artificial Neural Networks
Sign in. The zoo of neural network types grows exponentially. One needs a map to navigate between many emerging architectures and approaches. If you are not new to Machine Learning, you should have seen it before:. In this story, I will go through every mentioned topology and try to explain how it works and where it is used. The simplest an d oldest model of Neuron, as we know it.
Takes some inputs, sums them up, applies activation function and passes them to output layer. No magic here. Feed forward neural networks are also quite old — the approach originates from 50s. In most cases this type of networks is trained using Backpropagation method. RBF neural networks are actually FF feed forward NNs, that use radial basis function as activation function instead of logistic function. What makes the difference?
It is good for classification and decision making systems, but works bad for continuous values. This is perfect for function approximation, and machine control as a replacement of PID controllers, for example. To be short, these are just FF networks with different activation function and appliance. DFF neural networks opened pandora box of deep learning in early 90s.
These are just FF NNs, but with more than one hidden layer. So, what makes them so different? If you read my previous article on backpropagation, you may have noticed that, when training a traditional FF, we pass only a small amount of error to previous layer. Because of that stacking more layers led to exponential growth of training times, making DFFs quite impractical. Only in early 00s we developed a bunch of approaches that allowed to train DFFs effectively; now they form a core of modern Machine Learning systems, covering the same purposes as FFs, but with much better results.
Recurrent Neural Networks introduce different type of cells — Recurrent cells. Apart from that, it was like common FNN.
Of course, there are many variations — like passing the state to input nodes, variable delays, etc, but the main idea remains the same. This type of NNs is mainly used then context is important — when decisions from past iterations or samples can influence current ones.
The most common examples of such contexts are texts — a word can be analysed only in context of previous words or sentences. This type introduces a memory cell, a special cell that can process data when data have time gaps or lags.
LSTM networks are also widely used for writing and speech recognition. Memory cells are actually composed of a couple of elements — called gates, that are recurrent and control how information is being remembered and forgotten.
The structure is well seen in the wikipedia illustration note that there are no activation functions between blocks :. The x thingies on the graph are gates , and they have they own weights and sometimes activation functions. On each sample they decide whether to pass the data forward, erase memory and so on — you can read a quite more detailed explanation here.
Input gate decides how many information from last sample will be kept in memory; output gate regulate the amount of data passed to next layer, and forget gates control the tearing rate of memory stored. This is, however, a very simple implementation of LSTM cells, many others architectures exist.
Sounds simple, but lack of output gate makes it easier to repeat the same output for a concrete input multiple times, and are currently used the most in sound music and speech synthesis. The actual composition, though, is a bit different: all LSTM gates are combined into so-called update gate , and reset gate is closely tied to input. They are less resource consuming than LSTMs and almost the same effective. Autoencoders are used for classification, clustering and feature compression.
When you train FF neural networks for classification you mostly must feed then X examples in Y categories, and expect one of Y output cells to be activated.
AEs, on the other hand, can be trained without supervision. Their structure — when number of hidden cells is smaller than number of input cells and number of output cells equals number of input cells , and when the AE is trained the way the output is as close to input as possible, forces AEs to generalise data and search for common patterns. VAEs, comparing to AE, compress probabilities instead of features.
A little bit more in-depth explanation with some code is accessible here. While AEs are cool, they sometimes, instead of finding the most robust features, just adapt to input data it is actually an example of overfitting. DAEs add a bit of noise on the input cells — vary the data by random bit, randomly switch bits in input, etc.
By doing that, one forces DAE to reconstruct output from a bit noisy input, making it more general and forcing to pick more common features. SAE is yet another autoencoder type that in some cases can reveal some hidden grouping patters in data.
Markov Chains are pretty old concept of graphs where each edge has a probability. This MCs are not neural networks in a classic way, MCs can be used for classification based on probabilities like Bayesian filters , for clustering of some sort , and as a finite state machine.
Hopfield networks are trained on a limited set of samples so they respond to a known sample with the same sample. Each cell serves as input cell before training, as hidden cell during training and as output cell when used.
As HNs try to reconstruct the trained sample, they can be used for denoising and restoring inputs. Given a half of learned picture or sequence, they will return full sample. Boltzmann machines are very similar to HNs where some cells are marked as input and remain hidden. This is the first network topology that was succesfully tained using Simulated annealing approach. Multiple stacked Boltzmann Machines can for a so-called Deep belief network see below , that is used for feature detection and extraction.
RBMs resemble, in the structure, BMs but, due to being restricted, allow to be trained using backpropagation just as FFs with the only difference that before backpropagation pass data is passed back to input layer once. They can be chained together when one NN trains another and can be used to generate data by already learned pattern. DCN nowadays are stars of artificial neural networks.
They feature convolution cells or pooling layers and kernels, each serving a different purpose. Convolution kernels actually process input data, and pooling layers simplify it mostly using non-linear functions, like max , reducing unnecessary features. Typically used for image recognition, they operate on small subset of image something about 20x20 pixels. The input window is sliding along the image, pixel by pixel.
The data is passed to convolution layers, that form a funnel compressing detected features. From the terms of image recognition, first layer detects gradients, second lines, third shapes, and so on to the scale of particular objects. DFFs are commonly attached to the final convolutional layer for further data processing. DNs are DCNs reversed. DCN can take this vector and draw a cat image from that. I tried to find a solid demo, but the best demo is on youtube.
Actually, it is an autoencoder. DCN and DN do not act as separate networks, instead, they are spacers for input and output of the network. Mostly used for image processing, these networks can process images that they have not been trained with previously.
These nets, due to their abstraction levels, can remove certain objects from image, re-paint it, or replace horses with zebras like the famous CycleGAN did. GAN represents a huge family of double networks, that are composed from generator and discriminator. They constantly try to fool each other — generator tries to generate some data, and discriminator, receiving sample data, tries to tell generated data from samples.
Constantly evolving, this type of neural networks can generate real-life images, in case you are able to maintain the training balance between these two networks. LSM is sparse not fully connected neural network where activation functions are replaced by threshold levels.
Cell accumulates values from sequential samples, and emits output only when the threshold is reached, setting internal counter again to zero. Such idea is taken from human brain, and these networks are widely used in computer vision and speech recognition systems, but without major breakthroughs.
ELM is an attempt to reduce complexity behind FF networks by creating sparse hidden layers with random connections. They require less computational power, but the actual efficiency heavily depends on the task and data.
ESN is a subtype of recurrent networks with a special training approach. The data is passed to input, then the output if being monitored for multiple iterations allowing the recurrent features to kick in.
Only weights between hidden cells are updated after that. Personally, I know no real application of that type apart of multiple theoretical benchmarks.
Feel free to add yours. DRN is a deep network where some part of input data is passed to next layers. This feature allows them to be really deep up to layers , but actually they are kind of RNN without explicit delay. Mostly used for classification, this type of network tries to adjust their cells for maximal reaction to particular input. SVM is used for binary classification tasks. SVMs are not always considered to be a neural network. Huh, the last one!
Neural networks are kinda black-boxes — we can train them, get results, enhance them but the actual decision path is mostly hidden from us. Some authors also say that it is an abstraction over LSTM. The memory is addressed by its contents, and the network can read from and write to the memory depending on current state, representing a T uring-complete neural network.
Hope you liked this overview. If you think I made a mistake, feel free to comment, and subscribe for future articles about Machine Learning also, check my DIY AI series if interested in the topic.
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Artificial neural network
For example, variational autoencoders VAE may look just like autoencoders AE , but the training process is actually quite different. The use-cases for trained networks differ even more, because VAEs are generators, where you insert noise to get a new sample. It should be noted that while most of the abbreviations used are generally accepted, not all of them are. RNNs sometimes refer to recursive neural networks, but most of the time they refer to recurrent neural networks. So while this list may provide you with some insights into the world of AI, please, by no means take this list for being comprehensive; especially if you read this post long after it was written. For each of the architectures depicted in the picture, I wrote a very, very brief description.
Sign in. The zoo of neural network types grows exponentially. One needs a map to navigate between many emerging architectures and approaches. If you are not new to Machine Learning, you should have seen it before:. In this story, I will go through every mentioned topology and try to explain how it works and where it is used.
We apologize for the inconvenience...
But in some ways, a neural network is little more than several logistic regression models chained together. In this article, I try to explain to you in a comprehensive and mathematical way how a simple 2-layered neural network works, by coding one from scratch in Python. In the last layer we use the softmax activation function, since we wish to have probabilities of each class, so that we can measure how well our current forward pass performs. To do this you will need to install TensorFlow on your laptop or desktop by following this guide.. Neural Network from Scratch 1.
Humans and other animals process information with neural networks. These are formed from trillions of neurons nerve cells exchanging brief electrical pulses called action potentials. Computer algorithms that mimic these biological structures are formally called artificial neural networks to distinguish them from the squishy things inside of animals. However, most scientists and engineers are not this formal and use the term neural network to include both biological and nonbiological systems.
Collective intelligence Collective action Self-organized criticality Herd mentality Phase transition Agent-based modelling Synchronization Ant colony optimization Particle swarm optimization Swarm behaviour. Evolutionary computation Genetic algorithms Genetic programming Artificial life Machine learning Evolutionary developmental biology Artificial intelligence Evolutionary robotics. Reaction—diffusion systems Partial differential equations Dissipative structures Percolation Cellular automata Spatial ecology Self-replication. Rational choice theory Bounded rationality. Artificial neural networks ANNs , usually simply called neural networks NNs , are computing systems vaguely inspired by the biological neural networks that constitute animal brains.
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