EXPERT KNOWLEDGE AT A GLANCE

# Tag: artificialintelligence

The machine learning algorithm t-Distributed Stochastic Neighborhood Embedding, also abbreviated as t-SNE, can be used to visualize high-dimensional datasets. Each high-dimensional information of a
data point is reduced to a low-dimensional representation. However, the information about existing neighborhoods should be preserved.

So this technique is another tool you can use to create meaningful groups in unordered data collections based on the unifying data properties. If you don’t know what cluster algorithms are, check out this article. Here we present 5 machine learning methods that you should know.
As shown in the following figure, the data should be represented grouped in 2-dimensional space.

But how does the algorithm work and what are its strengths? In order to understand its function, we need to look at the origin of the technology.

#### What is the Stochastic Neighbor Embedding (SNE) Algorithm?

The basis of the t-Distributed Stochastic Neighborhood Embedding algorithm is originally the Stochastic Neighbor Embedding (SNE) algorithm. This converts high-dimensional Euclidean distances into similarity probabilities between individual data points.
The probability with which an object occurs next to a potential neighbor must be calculated.
The dissimilarities between two high-dimensional data points can be explained with a distance matrix, corresponding to the squared Euclidean distance.
A conditional probability is calculated for the low-dimensional correspondence.
This determines the similarity of the two data points on the low-dimensional map.

In order to achieve the closest possible correspondence between the two distributions pij and
qij, a Kullback-Leibler divergence (KL) over all neighbors of each data point is computed as a cost function C. Large costs are incurred for distant data points.

A gradient descent method is used to optimize the cost function. However, this optimization method converges very slowly. In addition, a so-called crowding problem arises.

If a high dimensional data set is linearly approximated in a small scale, then it cannot be reduced to a lower dimension with a local scaling algo-
rithm to a lower dimension.

#### What makes the t-Distributed Stochastic Neighborhood Embedding (t-SNE) Algorithmt work?

The t-Distributed Stochastic Neighbor
Embedding (t-SNE) algorithm starts here. On the one hand, a simplified symmetric cost function is used.

Here, only one KL is minimized over a common probability distribution of all
high, and low dimensional data is minimized.

On the other hand, the similarity of the low-dimensional data points is computed with a Student’s t-distribution and a degree of freedom of one. This can be optimized quickly and is stable to the crowding problem.
stable against the crowding problem.

It’s almost harder to understand all the acronyms around Artificial Intelligence (AI) than the technology itself.
AI vs Machine Learning vs Deep Learning – These terms are often carelessly mixed together. But what are actually the differences? In this article, we will introduce you to all Three fields, because even though there is overlap, they differ.
It should be important for you to know these differences, as each discipline describes different stages of a data analysis pipeline.

## AI vs Machine Learning vs Deep Learning

In the following figure, we have schematically shown you the individual fields in their context. As you can see, the individual disciplines surround each other and form an onion-like layered model.

The figure clearly shows that there are relationships between individual disciplines. AI is to be understood as a generic term and thus includes the other fields. The deeper you go in the model, the more specific the tasks become. In the following, we will follow this representation and work our way from the outside to the inside.

## Artificial intelligence

All disciplines are encompassed by the term AI. It is a science that explores ways to build intelligent programs and machines that can perceive, reason, act, and solve problems creatively. To this end, it attempts to model how the human brain works.
The following figure shows that AI can basically be divided into two categories.

Classification is about measuring the performance of AI based on how well it is able to replicate the human-like brain. In the Based on Functionality category, AI is classified based on how well it matches the human way of thinking. In the second category, it is evaluated based on human intelligence. Within these categories, there are still some subgroups that correspond to an index.

## AI vs Machine Learning

So what is the first subcategory Machine Learning and how does it differ from AI?
While AI deals with the functioning of artificial intelligence and compares them with the functioning of the human brain, machine learning is a collection of mathematical methods of pattern recognition. It is about how a system is given the ability to automatically learn and improve from experience. Various algorithms (e.g., neural networks) are used for this purpose. In the following scheme, the broad machine learning field is presented in a categorized way.

In machine learning, algorithms are used to build statistical models based on training data. Roughly, these algorithms can be divided into three main learning techniques. While in supervised learning the result is predetermined by a cleanly labeled data set, unsupervised learning is completely self-organized. Here the patterns are to be explored independently.
In reinforcement learning, utility functions are to be independently approximated based on rewards received.

## Machine Learning vs Deep Learning/ Deep Neural Learning

Deep learning is a subfield of machine learning similar to machine learning in Ai. Here, multilayer neural networks are used to analyze various factors in large amounts of data. These networks are similar to the human neural system. If you want to know more about this structure, read our article on perceptrons, the smallest unit of a neural network.
Optimization of neural weights, unlike machine learning, can be done using powerful GPUs. Pure machine learning is best used on structured data sets, while for unstructured data you should opt for deep learning. In the following graphic, we have summarized the main factors that make up deep learning. For the network types autoencoder and CNN we provide more detailed articles.

AutoEncoder – In data science, we often encounter multidimensional data relationships. Understanding and representing these is often not straightforward. But how do you effectively reduce the dimension without reducing the information content?

## Unsupervised dimension reduction

One possibility is offered by unsupervised machine learning algorithms, which aim to code high-dimensional data as effectively as possible in a low-dimensional way.
If you don’t know the difference between unsupervised, supervised and reinforcement learning, check out this article we wrote on the topic.

## What is an AutoEncoder?

The AutoEncoder is an artificial neural network that is used to unsupervised reduce the data dimensions.
The network usually consists of three or more layers. The gradient calculation is usually done with a backpropagation algorithm. The network thus corresponds to a feedforward network that is fully interconnected layer by layer.

## Types

AutoEncoder types are many. The following table lists the most common variations.

However, the basic structure of all variations is the same for all types.

## Basic Structure

Each AutoEncoder is characterized by an encoding and a decoding side, which are connected by a bottleneck, a much smaller hidden layer.

The following figure shows the basic network structure.

During encoding, the dimension of the input information is reduced. The average value of the information is passed on and the information is compressed in such a way.
In the decoding part, the compressed information is to be used to reconstruct the original data. For this purpose, the weights are then adjusted via backpropagation.
In the output layer, each neuron then has the same meaning as the corresponding neuron in the input layer.

## Autoencoder vs Restricted Boltzmann Machine (RBM)

Restricted Boltzmann Machines are also based on a similar idea. These are undirected graphical models useful for dimensionality reduction, classification, regression, collaborative filtering, and feature learning. However, these take a stochastic approach. Thus, stochastic units with a particular distribution are used instead of the deterministic distribution.

RBMs are designed to find the connections between visible and hidden random variables. How does the training work?
The hidden biases generate the activations during forward traversal and the visible layer biases generate learning of the reconstruction during backward traversal.

## Pretraining

Since the random initialization of weights in neural networks at the beginning of training is not always optimal, it makes sense to pre-train. The task of training is to minimize an error or a reconstruction in order to find the most efficient compact representation for input data.

The method was developed by Geoffrey Hinton and is primarily for training complex autoencoders. Here, the neighboring layers are treated as a Restricted Boltzmann Machine. Thus, a good approximation is achieved and fine-tuning is done with a backpropagation.

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