Types of clustering and different types of clustering algorithmsPrashanth Guntal
?
The document discusses different types of clustering algorithms:
1. Hard clustering assigns each data point to one cluster, while soft clustering allows points to belong to multiple clusters.
2. Hierarchical clustering builds clusters hierarchically in a top-down or bottom-up approach, while flat clustering does not have a hierarchy.
3. Model-based clustering models data using statistical distributions to find the best fitting model.
It then provides examples of specific clustering algorithms like K-Means, Fuzzy K-Means, Streaming K-Means, Spectral clustering, and Dirichlet clustering.
This document discusses unsupervised machine learning techniques for clustering unlabeled data. It covers k-means clustering, which partitions data into k groups based on minimizing distance between points and cluster centroids. It also discusses agglomerative hierarchical clustering, which successively merges clusters based on their distance. As an example, it shows hierarchical clustering of texture images from five classes to group similar textures.
This document provides an overview of clustering techniques. It introduces partitioning methods like k-means and k-medoids, hierarchical methods including agglomerative and divisive approaches, model-based methods using mixtures of Gaussians and expectation-maximization, and density-based techniques such as DBSCAN. It discusses applications of clustering, evaluates clustering quality, and covers requirements and challenges for clustering large datasets.
This document discusses clustering methods using the EM algorithm. It begins with an overview of machine learning and unsupervised learning. It then describes clustering, k-means clustering, and how k-means can be formulated as an optimization of a biconvex objective function solved via an iterative EM algorithm. The document goes on to describe mixture models and how the EM algorithm can be used to estimate the parameters of a Gaussian mixture model (GMM) via maximum likelihood.
A presentation about NGBoost (Natural Gradient Boosting) which I presented in the Information Theory and Probabilistic Programming course at the University of Oklahoma.
Classification of common clustering algorithm and techniques, e.g., hierarchical clustering, distance measures, K-means, Squared error, SOFM, Clustering large databases.
This document provides an overview of clustering analysis techniques, including k-means clustering, DBSCAN clustering, and self-organizing maps (SOM). It defines clustering as the process of grouping similar data points together. K-means clustering partitions data into k clusters by finding cluster centroids. DBSCAN identifies clusters based on density rather than specifying the number of clusters. SOM projects high-dimensional data onto a low-dimensional grid using a neural network approach.
How Machine Learning Helps Organizations to Work More Efficiently?Tuan Yang
?
Data is increasing day by day and so is the cost of data storage and handling. However, by understanding the concepts of machine learning one can easily handle the excessive data and can process it in an affordable manner.
The process includes making models by using several kinds of algorithms. If the model is created precisely for certain task, then the organizations have a very wide chance of making use of profitable opportunities and avoiding the risks lurking behind the scenes.
Learn more about:
? Understanding Machine Learning Objectives.
? Data dimensions in Machine Learning.
? Fundamentals of Algorithms and Mapping from Input/Output.
? Parametric and Non-parametric Machine Learning Algorithms.
? Supervised, Unsupervised and Semi-Supervised Learning.
? Estimating Over-fitting and Under-fitting.
? Use Cases.
Lecture 18: Gaussian Mixture Models and Expectation Maximizationbutest
?
This document discusses Gaussian mixture models (GMMs) and the expectation-maximization (EM) algorithm. GMMs model data as coming from a mixture of Gaussian distributions, with each data point assigned soft responsibilities to the different components. EM is used to estimate the parameters of GMMs and other latent variable models. It iterates between an E-step, where responsibilities are computed based on current parameters, and an M-step, where new parameters are estimated to maximize the expected complete-data log-likelihood given the responsibilities. EM converges to a local optimum for fitting GMMs to data.
The document discusses several machine learning algorithms: Kohonen's self-organizing map (SOM) which reduces dimensionality; K-means clustering which groups similar data points; logistic regression which classifies data using probabilities; support vector machines (SVM) which find optimal separating hyperplanes; C4.5 decision trees which classify using a question-answer tree structure; random forests which create many decision trees; gradient boosting decision trees which iteratively adjust weights; and K-nearest neighbors (KNN) which classifies based on closest training examples. For each algorithm, it provides a brief overview of the approach and key steps or equations involved.
Mean shift clustering finds clusters by locating peaks in the probability density function of the data. It iteratively moves data points to the mean of nearby points until convergence. Hierarchical clustering builds clusters gradually by either merging or splitting clusters at each step. There are two types: divisive which splits clusters, and agglomerative which merges clusters. Agglomerative clustering starts with each point as a cluster and iteratively merges the closest pair of clusters until all are merged based on a chosen linkage method like complete or average linkage. The choice of distance metric and linkage method impacts the resulting clusters.
Part 2: Unsupervised Learning Machine Learning Techniques butest
?
This document summarizes unsupervised learning techniques for computer vision, including:
1) Gaussian mixture models and the EM algorithm for clustering with discrete latent variables.
2) Probabilistic PCA and related methods for dimensionality reduction using continuous latent variables.
3) Variational inference techniques like variational Bayes for approximating intractable posteriors.
This document provides an overview of the gradient boosted machines (GBM) package in R. It begins with an outline of the presentation and then defines GBM as an algorithm that combines multiple decision trees through gradient boosting and iteration to minimize residuals. It notes that GBM can perform classification or regression tasks and has competitive performance, robustness, and the ability to handle different loss functions. The document then discusses GBM's decision tree structure, performance advantages over other algorithms, tuning parameters, and tools for analyzing fitted GBM models. Code examples are also provided to demonstrate fitting and evaluating a GBM model on a dataset.
Optimization as a model for few shot learningKaty Lee
?
paper presentation of "Optimization as a model for few shot learning" at ICLR 2017 by Sachin Ravi and Hugo Larochelle
highly related to "learning to learn by gradient descent by gradient descent"
This document discusses various clustering methods used in data mining. It begins with an overview of clustering and its applications. It then describes five major categories of clustering methods: partitioning methods like k-means and k-medoids, hierarchical methods like agglomerative nesting and divisive analysis, density-based methods, grid-based methods, and model-based clustering methods. For each category, popular algorithms are provided as examples. The document also covers types of data for clustering and evaluating clustering results.
Cluster analysis, or clustering, is the process of grouping data objects into subsets called clusters so that objects within a cluster are similar to each other but dissimilar to objects in other clusters. There are several approaches to clustering, including partitioning, hierarchical, density-based, and grid-based methods. The k-means and k-medoids algorithms are popular partitioning methods that aim to partition observations into k clusters by minimizing distances between observations and cluster centroids or medoids. K-medoids is more robust to outliers as it uses actual observations as cluster representatives rather than centroids. Both methods require specifying the number of clusters k in advance.
Cluster analysis is an unsupervised learning technique used to group similar objects together. It identifies clusters of objects such that objects within a cluster are more closely related to each other than objects in different clusters. Common applications of cluster analysis include document clustering, market segmentation, and identifying types of customers or animals. Popular clustering algorithms include k-means, k-medoids, hierarchical clustering, density-based clustering, and grid-based clustering.
Hierarchical clustering methods build groups of objects in a recursive manner through either an agglomerative or divisive approach. Agglomerative clustering starts with each object in its own cluster and merges the closest pairs of clusters until only one cluster remains. Divisive clustering starts with all objects in one cluster and splits clusters until each object is in its own cluster. DBSCAN is a density-based clustering method that identifies core, border, and noise points based on a density threshold. OPTICS improves upon DBSCAN by producing a cluster ordering that contains information about intrinsic clustering structures across different parameter settings.
This document provides an overview of clustering and k-means clustering algorithms. It begins by defining clustering as the process of grouping similar objects together and dissimilar objects separately. K-means clustering is introduced as an algorithm that partitions data points into k clusters by minimizing total intra-cluster variance, iteratively updating cluster means. The k-means algorithm and an example are described in detail. Weaknesses and applications are discussed. Finally, vector quantization and principal component analysis are briefly introduced.
Big data Clustering Algorithms And StrategiesFarzad Nozarian
?
The document discusses various algorithms for big data clustering. It begins by covering preprocessing techniques such as data reduction. It then covers hierarchical, prototype-based, density-based, grid-based, and scalability clustering algorithms. Specific algorithms discussed include K-means, K-medoids, PAM, CLARA/CLARANS, DBSCAN, OPTICS, MR-DBSCAN, DBCURE, and hierarchical algorithms like PINK and l-SL. The document emphasizes techniques for scaling these algorithms to large datasets, including partitioning, sampling, approximation strategies, and MapReduce implementations.
The document provides an overview of clustering methods and algorithms. It defines clustering as the process of grouping objects that are similar to each other and dissimilar to objects in other groups. It discusses existing clustering methods like K-means, hierarchical clustering, and density-based clustering. For each method, it outlines the basic steps and provides an example application of K-means clustering to demonstrate how the algorithm works. The document also discusses evaluating clustering results and different measures used to assess cluster validity.
This document provides an overview of clustering analysis techniques, including k-means clustering, DBSCAN clustering, and self-organizing maps (SOM). It defines clustering as the process of grouping similar data points together. K-means clustering partitions data into k clusters by finding cluster centroids. DBSCAN identifies clusters based on density rather than specifying the number of clusters. SOM projects high-dimensional data onto a low-dimensional grid using a neural network approach.
How Machine Learning Helps Organizations to Work More Efficiently?Tuan Yang
?
Data is increasing day by day and so is the cost of data storage and handling. However, by understanding the concepts of machine learning one can easily handle the excessive data and can process it in an affordable manner.
The process includes making models by using several kinds of algorithms. If the model is created precisely for certain task, then the organizations have a very wide chance of making use of profitable opportunities and avoiding the risks lurking behind the scenes.
Learn more about:
? Understanding Machine Learning Objectives.
? Data dimensions in Machine Learning.
? Fundamentals of Algorithms and Mapping from Input/Output.
? Parametric and Non-parametric Machine Learning Algorithms.
? Supervised, Unsupervised and Semi-Supervised Learning.
? Estimating Over-fitting and Under-fitting.
? Use Cases.
Lecture 18: Gaussian Mixture Models and Expectation Maximizationbutest
?
This document discusses Gaussian mixture models (GMMs) and the expectation-maximization (EM) algorithm. GMMs model data as coming from a mixture of Gaussian distributions, with each data point assigned soft responsibilities to the different components. EM is used to estimate the parameters of GMMs and other latent variable models. It iterates between an E-step, where responsibilities are computed based on current parameters, and an M-step, where new parameters are estimated to maximize the expected complete-data log-likelihood given the responsibilities. EM converges to a local optimum for fitting GMMs to data.
The document discusses several machine learning algorithms: Kohonen's self-organizing map (SOM) which reduces dimensionality; K-means clustering which groups similar data points; logistic regression which classifies data using probabilities; support vector machines (SVM) which find optimal separating hyperplanes; C4.5 decision trees which classify using a question-answer tree structure; random forests which create many decision trees; gradient boosting decision trees which iteratively adjust weights; and K-nearest neighbors (KNN) which classifies based on closest training examples. For each algorithm, it provides a brief overview of the approach and key steps or equations involved.
Mean shift clustering finds clusters by locating peaks in the probability density function of the data. It iteratively moves data points to the mean of nearby points until convergence. Hierarchical clustering builds clusters gradually by either merging or splitting clusters at each step. There are two types: divisive which splits clusters, and agglomerative which merges clusters. Agglomerative clustering starts with each point as a cluster and iteratively merges the closest pair of clusters until all are merged based on a chosen linkage method like complete or average linkage. The choice of distance metric and linkage method impacts the resulting clusters.
Part 2: Unsupervised Learning Machine Learning Techniques butest
?
This document summarizes unsupervised learning techniques for computer vision, including:
1) Gaussian mixture models and the EM algorithm for clustering with discrete latent variables.
2) Probabilistic PCA and related methods for dimensionality reduction using continuous latent variables.
3) Variational inference techniques like variational Bayes for approximating intractable posteriors.
This document provides an overview of the gradient boosted machines (GBM) package in R. It begins with an outline of the presentation and then defines GBM as an algorithm that combines multiple decision trees through gradient boosting and iteration to minimize residuals. It notes that GBM can perform classification or regression tasks and has competitive performance, robustness, and the ability to handle different loss functions. The document then discusses GBM's decision tree structure, performance advantages over other algorithms, tuning parameters, and tools for analyzing fitted GBM models. Code examples are also provided to demonstrate fitting and evaluating a GBM model on a dataset.
Optimization as a model for few shot learningKaty Lee
?
paper presentation of "Optimization as a model for few shot learning" at ICLR 2017 by Sachin Ravi and Hugo Larochelle
highly related to "learning to learn by gradient descent by gradient descent"
This document discusses various clustering methods used in data mining. It begins with an overview of clustering and its applications. It then describes five major categories of clustering methods: partitioning methods like k-means and k-medoids, hierarchical methods like agglomerative nesting and divisive analysis, density-based methods, grid-based methods, and model-based clustering methods. For each category, popular algorithms are provided as examples. The document also covers types of data for clustering and evaluating clustering results.
Cluster analysis, or clustering, is the process of grouping data objects into subsets called clusters so that objects within a cluster are similar to each other but dissimilar to objects in other clusters. There are several approaches to clustering, including partitioning, hierarchical, density-based, and grid-based methods. The k-means and k-medoids algorithms are popular partitioning methods that aim to partition observations into k clusters by minimizing distances between observations and cluster centroids or medoids. K-medoids is more robust to outliers as it uses actual observations as cluster representatives rather than centroids. Both methods require specifying the number of clusters k in advance.
Cluster analysis is an unsupervised learning technique used to group similar objects together. It identifies clusters of objects such that objects within a cluster are more closely related to each other than objects in different clusters. Common applications of cluster analysis include document clustering, market segmentation, and identifying types of customers or animals. Popular clustering algorithms include k-means, k-medoids, hierarchical clustering, density-based clustering, and grid-based clustering.
Hierarchical clustering methods build groups of objects in a recursive manner through either an agglomerative or divisive approach. Agglomerative clustering starts with each object in its own cluster and merges the closest pairs of clusters until only one cluster remains. Divisive clustering starts with all objects in one cluster and splits clusters until each object is in its own cluster. DBSCAN is a density-based clustering method that identifies core, border, and noise points based on a density threshold. OPTICS improves upon DBSCAN by producing a cluster ordering that contains information about intrinsic clustering structures across different parameter settings.
This document provides an overview of clustering and k-means clustering algorithms. It begins by defining clustering as the process of grouping similar objects together and dissimilar objects separately. K-means clustering is introduced as an algorithm that partitions data points into k clusters by minimizing total intra-cluster variance, iteratively updating cluster means. The k-means algorithm and an example are described in detail. Weaknesses and applications are discussed. Finally, vector quantization and principal component analysis are briefly introduced.
Big data Clustering Algorithms And StrategiesFarzad Nozarian
?
The document discusses various algorithms for big data clustering. It begins by covering preprocessing techniques such as data reduction. It then covers hierarchical, prototype-based, density-based, grid-based, and scalability clustering algorithms. Specific algorithms discussed include K-means, K-medoids, PAM, CLARA/CLARANS, DBSCAN, OPTICS, MR-DBSCAN, DBCURE, and hierarchical algorithms like PINK and l-SL. The document emphasizes techniques for scaling these algorithms to large datasets, including partitioning, sampling, approximation strategies, and MapReduce implementations.
The document provides an overview of clustering methods and algorithms. It defines clustering as the process of grouping objects that are similar to each other and dissimilar to objects in other groups. It discusses existing clustering methods like K-means, hierarchical clustering, and density-based clustering. For each method, it outlines the basic steps and provides an example application of K-means clustering to demonstrate how the algorithm works. The document also discusses evaluating clustering results and different measures used to assess cluster validity.
Introduction to Machine Learning Lecturesssuserfece35
?
This lecture discusses ensemble methods in machine learning. It introduces bagging, which trains multiple models on random subsets of the training data and averages their predictions, in order to reduce variance and prevent overfitting. Bagging is effective because it decreases the correlation between predictions. Random forests apply bagging to decision trees while also introducing more randomness by selecting a random subset of features to consider at each node. The next lecture will cover boosting, which aims to reduce bias by training models sequentially to focus on examples previously misclassified.
Infervision is a company that uses artificial intelligence to help doctors by automatically recognizing symptoms on medical images and recommending treatments. Their goal is to make top medical expertise available to everyone by reducing the burden on doctors and improving access to healthcare in rural areas. They have developed powerful AI models for various diseases by combining deep learning with medical data from partner hospitals in China. Their products help generate diagnostic reports and can screen for diseases to improve efficiency and lower healthcare costs.
Transformer in Medical Imaging A brief reviewssuserfece35
?
Transformers show promise for medical imaging tasks by enabling long-range modeling via self-attention. Two papers presented techniques using transformers for robust fovea localization and multi-lesion segmentation. The first used a transformer block to fuse retinal image and vessel features. The second used relation blocks modeling interactions between lesions and between lesions and vessels, improving hard-to-segment lesion detection. Efficient transformers like Swin and deformable sampling were also discussed, enabling long-range modeling with reduced complexity for 3D tasks. Overall, transformers appear well-suited for medical imaging by capturing global context but efficient techniques are needed for 3D applications.
Viceroys of India & Their Tenure ¨C Key Events During British RuleDeeptiKumari61
?
The British Raj in India (1857-1947) saw significant events under various Viceroys, shaping the political, economic, and social landscape.
**Early Period (1856-1888):**
Lord Canning (1856-1862) handled the Revolt of 1857, leading to the British Crown taking direct control. Universities were established, and the Indian Councils Act (1861) was passed. Lord Lawrence (1864-1869) led the Bhutan War and established High Courts. Lord Lytton (1876-1880) enforced repressive laws like the Vernacular Press Act (1878) and Arms Act (1878) while waging the Second Afghan War.
**Reforms & Political Awakening (1880-1905):**
Lord Ripon (1880-1884) introduced the Factory Act (1881), Local Self-Government Resolution (1882), and repealed the Vernacular Press Act. Lord Dufferin (1884-1888) oversaw the formation of the Indian National Congress (1885). Lord Lansdowne (1888-1894) passed the Factory Act (1891) and Indian Councils Act (1892). Lord Curzon (1899-1905) introduced educational reforms but faced backlash for the Partition of Bengal (1905).
**Rise of Nationalism (1905-1931):**
Lord Minto II (1905-1910) saw the rise of the Swadeshi Movement and the Muslim League's formation (1906). Lord Hardinge II (1910-1916) annulled Bengal¡¯s Partition (1911) and shifted India¡¯s capital to Delhi. Lord Chelmsford (1916-1921) faced the Lucknow Pact (1916), Jallianwala Bagh Massacre (1919), and Non-Cooperation Movement. Lord Reading (1921-1926) dealt with the Chauri Chaura Incident (1922) and the formation of the Swaraj Party. Lord Irwin (1926-1931) saw the Simon Commission protests, the Dandi March, and the Gandhi-Irwin Pact (1931).
**Towards Independence (1931-1947):**
Lord Willingdon (1931-1936) introduced the Government of India Act (1935), laying India's federal framework. Lord Linlithgow (1936-1944) faced WWII-related crises, including the Quit India Movement (1942). Lord Wavell (1944-1947) proposed the Cabinet Mission Plan (1946) and negotiated British withdrawal. Lord Mountbatten (1947-1948) oversaw India's Partition and Independence on August 15, 1947.
**Final Transition:**
C. Rajagopalachari (1948-1950), India¡¯s last Governor-General, facilitated India¡¯s transition into a republic before the position was abolished in 1950.
The British Viceroys played a crucial role in India¡¯s colonial history, introducing both repressive and progressive policies that fueled nationalist movements, ultimately leading to independence.https://www.youtube.com/@DKDEducation
Stages of combustion, Ignition lag, Flame propagation, Factors affecting flame
speed, Abnormal combustion, Influence of engine design and operating
variables on detonation, Fuel rating, Octane number, Fuel additives, HUCR,
Requirements of combustion chambers of S.I. Engines and its types.
Unit1 Inroduction to Internal Combustion EnginesNileshKumbhar21
?
Introduction of I. C. Engines, Types of engine, working of engine, Nomenclature of engine, Otto cycle, Diesel cycle Fuel air cycles Characteristics of fuel - air mixtures Actual cycles, Valve timing diagram for high and low speed engine, Port timing diagram
Measles Outbreak¡ªSouthwestern US¡ª This briefing reviews the current situation surrounding the measles outbreaks in Texas, New Mexico, Oklahoma, and Kansas.
General College Quiz conducted by Pragya the Official Quiz Club of the University of Engineering and Management Kolkata in collaboration with Ecstasia the official cultural fest of the University of Engineering and Management Kolkata.
Unit No 4- Chemotherapy of Malignancy.pptxAshish Umale
?
In the Pharmacy profession there are many dangerous diseases from which the most dangerous is cancer. Here we study about the cancer as well as its treatment that is supportive to the students of semester VI of Bachelor of Pharmacy. Cancer is a disease of cells of characterized by Progressive, Persistent, Perverted (abnormal), Purposeless and uncontrolled Proliferation of tissues. There are many types of cancer that are harmful to the human body which are responsible to cause the disease condition. The position 7 of guanine residues in DNA is especially susceptible. Cyclophosphamide is a prodrug converted to the active metabolite aldophosphamide in the liver. Procarbazine is a weak MAO inhibitor; produces sedation and other CNS effects, and can interact with foods and drugs. Methotrexate is one of the most commonly used anticancer drugs. Methotrexate (MTX) is a folic acid antagonist. 6-MP and 6-TG are activated to their ribonucleotides, which inhibit purine ring biosynthesis and nucleotide inter conversion. Pyrimidine analogue used in antineoplastic, antifungal and anti psoriatic agents.
5-Fluorouracil (5-FU) is a pyrimidine analog. It is a complex diterpin taxane obtained from bark of the Western yew tree. Actinomycin D is obtained from the fungus of Streptomyces species. Gefitinib and Erlotinib inhibit epidermal growth factor receptor (EGFR) tyrosine kinase. Sunitinib inhibits multiple receptor tyrosine kinases like platelet derived growth factor (PDGF) Rituximab target antigen on the B cells causing lysis of these cells.
Prednisolone is 4 times more potent than hydrocortisone, also more selective glucocorticoid, but fluid retention does occur with high doses. Estradiol is a major regulator of growth for the subset of breast cancers that express the estrogen receptor (ER, ESR1).
Finasteride and dutasteride inhibit conversion of testosterone to dihydrotestosterone in prostate (and other tissues), have palliative effect in advanced carcinoma prostate; occasionally used. Chemotherapy in most cancers (except curable cancers) is generally palliative and suppressive. Chemotherapy is just one of the modes in the treatment of cancer. Other modes like radiotherapy and surgery are also employed to ensure 'total cell kill'.
Design approaches and ethical challenges in Artificial Intelligence tools for...Yannis
?
The recent technology of Generative Artificial Intelligence (GenAI) has undeniable advantages, especially with regard to improving the efficiency of all stakeholders in the education process.
At the same time, almost all responsible international organisations and experts in the field of education and educational technology point out a multitude of general ethical problems that need to be addressed. Many of these problems have already arisen in previous models of artificial intelligence or even in systems based on learning data, and several are appearing for the first time.
In this short contribution, we will briefly review some dimensions of ethical problems, both (a) the general ones related to trust, transparency, privacy, personal data security, accountability, environmental responsibility, bias, power imbalance, etc., and (b) the more directly related to teaching, learning, and education, such as students' critical thinking, the social role of education, the development of teachers' professional competences, etc.
In addition, the categorizations of possible service allocation to humans and AI tools, the human-centered approach to designing AI tools and learning data, as well as the more general design of ethics-aware applications and activities will be briefly presented. Finally, some short illustrative examples will be presented to set the basis for the debate in relation to ethical and other dilemmas.
Chapter 6. Business and Corporate Strategy Formulation.pdfRommel Regala
?
This integrative course examines the strategic decision-making processes of top management,
focusing on the formulation, implementation, and evaluation of corporate strategies and policies.
Students will develop critical thinking and analytical skills by applying strategic frameworks,
conducting industry and environmental analyses, and exploring competitive positioning. Key
topics include corporate governance, business ethics, competitive advantage, and strategy
execution. Through case studies and real-world applications, students will gain a holistic
understanding of strategic management and its role in organizational success, preparing them to
navigate complex business environments and drive strategic initiatives effectively.
Anorectal malformations refer to a range of congenital anomalies that involve the anus, rectum, and sometimes the urinary and genital organs. They result from abnormal development during the embryonic stage, leading to incomplete or absent formation of the rectum, anus, or both.
How to Install Odoo 18 with Pycharm - Odoo 18 ºÝºÝߣsCeline George
?
In this slide we¡¯ll discuss the installation of odoo 18 with pycharm. Odoo 18 is a powerful business management software known for its enhanced features and ability to streamline operations. Built with Python 3.10+ for the backend and PostgreSQL as its database, it provides a reliable and efficient system.
2. 2
Acknowledges
This set of lecture notes has been adapted from
materials originally provided by Dr. Gan Hong Seng and
Christopher M. Bishop's lecture notes.
3. 3
Course Outline
? What it is GMM?
? The concept of Mixture of Gaussians
? EM algorithm & Latent Variables l,
4. 4
What is Gaussian Mixture Model?
? Probabilistic Model used for clustering and classification tasks.
? Assumption: data is generated by a mixture of several Gaussian
distributions, each with its own mean and variance.
? Application: by fitting a GMM to the data:
? Identify underlying clusters.
? Make predictions on new data points through probabilistic
assignments to each cluster..
? What is Gaussian Mixture Model
5. 5
Example of Gaussian Distribution
X-Axis: Data Values
Y-Axis: Frequency or Probability of Occurrence
? Bell-Shaped Curve: illustrates that most data is clustered around the mean.
? Mean is depicted by the vertical line at the center.
? Standard Deviation measures the spread of the data
8. Likelihood Function
? Data set
? The probability of observing x given the Gaussian distribution:
Assume observed data points generated independently
? This probability is a function of the parameters this is known as the
likelihood function
9. Maximum Likelihood
? Obtaining the parameters by the given dataset, and maximizing the
likelihood function
? Equivalently maximize the log likelihood
10. Maximum Likelihood Solution
? Maximizing w.r.t. the mean gives the sample mean
? Maximizing w.r.t covariance gives the sample covariance
11. 11
Mixture Models
? So estimating parameters for a single Gaussian is simple.
? How about modelling non-Gaussian data?
? Mixture models can be powerful to handle many non-gaussian data
distributions!
12. 12
Mixture Model
Mixture Models are a collection of the weighted sum of a number of
probability density functions (PDFs) where the weights are determined by a
distribution
14. 14
Hard Assignments (K-Means Clustering)
? Exclusive Assignment: each data point is assigned to a single
cluster.
? Cluster Membership: data points belong to one, and only
one, cluster.
15. 15
Soft Assignments (GMM)
? Probabilistic Assignment: Assigns a probability for each data point
indicating its likelihood of belonging to each Gaussian distribution in
the mixture.
? Partial Membership: A single data point can have partial membership
in multiple Gaussian distributions.
16. 16
Q&A
? When to use hard assignment and when to use soft assignment?
17. 17
Hard vs Soft Assignemnts
? When to Use Hard Assignments
? Ideal for data with clearly separable, distinct clusters.
? Most effective when there is minimal overlap between clusters.
? When to Use Soft Assignments
? Suitable for data that is not easily separable into distinct clusters.
? Ideal for handling data with significant overlap between clusters.
20. 20
Mixture of Gaussian in 2D
? Model Assumption: Data points are generated by a combination of several 2D Gaussian distributions.
? Distinct Parameters: Each distribution has its own mean (center point) and covariance matrix (shape and
orientation).
26. Gaussian Mixtures
? Linear super-position of Gaussians
? Normalization and positivity require
? Can interpret the mixing coefficients as prior probabilities
27. Sampling from the Gaussian Mixture
? To generate a data point:
? first pick one of the components with probability
? then draw a sample from that component
? Repeat these two steps for each new data point
28. Fitting the Gaussian Mixture
? We wish to invert this process ¨C given the data set, find the
corresponding parameters:
? mixing coefficients
? means
? covariances
? If we knew which component generated each data point, the
maximum likelihood solution would involve fitting each component to
the corresponding cluster
? Problem: the data set is unlabelled
? We shall refer to the labels as latent (= hidden) variables
30. Posterior Probabilities
? We can think of the mixing coefficients as prior probabilities for the
components
? For a given value of we can evaluate the corresponding posterior
probabilities, called responsibilities
? These are given from Bayes¡¯ theorem by
33. Maximum Likelihood for the GMM
? The log likelihood function takes the form
? Note: sum over components appears inside the log
? There is no closed form solution for maximum likelihood
34. Problems and Solutions
? How to maximize the log likelihood
? solved by expectation-maximization (EM) algorithm
? This is the topic of our lecture
? How to avoid singularities in the likelihood function
? solved by a Bayesian treatment
? How to choose number K of components
? also solved by a Bayesian treatment
35. EM Algorithm ¨C Informal Derivation
? Let us proceed by simply differentiating the log likelihood
? Setting derivative with respect to equal to zero gives
giving
which is simply the weighted mean of the data
36. EM Algorithm ¨C Informal Derivation
? Similarly for the covariances
? For mixing coefficients use a Lagrange multiplier to give
40. EM Algorithm ¨C Informal Derivation
? An iterative scheme for solving them:
? Make initial guesses for the parameters
? Alternate between the following two stages:
1. E-step: evaluate responsibilities
2. M-step: update parameters using ML results
47. 47
GMM and K-Means Differences
K-means Clustering
? Assumption: Spherical clusters with equal probability.
? Cluster Assignment: Hard assignment (points belong to one cluster).
? Cluster Shape: Only identifies circular clusters.
? Algorithm: Minimizes within-cluster variance.
? Outlier Sensitivity: High, due to mean calculation.
Gaussian Mixture Models (GMM)
? Assumption: Data from multiple Gaussian distributions.
? Cluster Assignment: Soft assignment (probabilistic cluster
membership).
? Cluster Shape: Identifies elliptical clusters.
? Algorithm: Maximizes likelihood using expectation-maximization.
? Outlier Sensitivity: Lower, due to probabilistic framework.
48. 48
GMM and K-Means Differences
Flexibility in Cluster Shapes: GMM can model elliptical and varying size clusters, not
just spherical.
Soft Clustering and Uncertainty: Provides membership probabilities, offering a
nuanced understanding of cluster belonging.
Density Estimation: GMM estimates the density distribution of each cluster, not just
central tendency.
Model Complexity: GMM captures complex cluster structures but requires more data
and computational power.
49. 49
GMM and K-Means Differences
Use K-means When:
? You need a fast, simple, and interpretable model.
? Your data is expected to form spherical clusters.
? Computational resources are limited.
Use GMM When:
? You suspect clusters are non-spherical or have different sizes.
? You need a measure of uncertainty in cluster assignments.
? You have enough data to estimate the additional parameters reliably.
Takeaway:
? K-means is efficient for well-separated, spherical clusters.
? GMM is more flexible, capturing complex cluster shapes and providing
probabilistic cluster assignments.
Editor's Notes
#4: In the realm of statistical analysis, the Gaussian Mixture Model (GMM) is a versatile probabilistic tool that serves both for clustering and classification tasks. It operates under the assumption that the data points are produced by a blend of multiple Gaussian distributions, each characterized by distinct parameters¡ªmean and variance that define their centers and spreads, respectively. By applying a GMM to a dataset, we can uncover latent groupings inherent in the data, revealing the underlying structure. Furthermore, the model empowers us to make informed predictions about where new data points might belong within these clusters, not through rigid assignment but by calculating the likelihood of membership in each cluster, thereby yielding a more nuanced, probabilistic classification.
#47: K-means operates on the assumption that each cluster is spherical and all clusters are equally likely, assigning each data point to a single cluster in a 'hard' manner, meaning points are fully in one cluster or another. This algorithm seeks to make the variation within each cluster as small as possible, but it tends to be sensitive to outliers because it uses the mean of the points to determine cluster centers and can only identify circular-shaped clusters. On the other hand, GMM assumes that data points are drawn from several Gaussian distributions, which allows for 'soft' cluster assignment. This means that it assigns points to clusters based on the probability of membership, making it more flexible in accommodating elliptical cluster shapes. The GMM algorithm uses an expectation-maximization process to maximize the likelihood of the data points given the model, and it is generally less sensitive to outliers due to its probabilistic nature.
#48: In academic discourse, the Gaussian Mixture Model (GMM) is prized for its flexibility in capturing a wide variety of cluster shapes, including elliptical forms and clusters of different sizes, rather than being confined to identifying only spherical clusters as some other methods are. GMM extends beyond simple cluster assignment by providing membership probabilities for each data point, thereby offering a more sophisticated and nuanced view of how data points relate to potential clusters. This model excels in estimating the density distribution within each cluster, which provides a richer understanding than merely pinpointing the central tendency. However, the intricacy of GMM in modeling complex cluster configurations comes at a cost; it necessitates a larger dataset and more computational resources to perform effectively.
#49: Choose K-means if you're looking for a quick, straightforward method that's easy to explain and when you think your data naturally splits into neat, round groups. It's also a good pick when you don't have a lot of computing power. On the other hand, go for the Gaussian Mixture Model (GMM) when you have a hunch that your clusters aren't just simple spheres or when they come in different sizes. GMM is also helpful when you want to know how sure the model is about which group each piece of data belongs to, but remember, it needs a good amount of data to work properly. To sum it up, K-means is your go-to for quick and clean clustering of round groups, while GMM is the choice for more complex situations and gives you insights into the probability of each data point's membership in a cluster.