# Supervised Vs Unsupervised Learning Fundamentals

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## 7 Questions

### Match the following machine learning tasks with their descriptions:

Supervised Learning = Training examples have provided labels Unsupervised Learning = No labels provided for each training example Clustering = Grouping similar data points together Anomaly detection = Identifying abnormal or unusual data points

### Match the following dimensionality reduction techniques with their descriptions:

Principle Component Analysis (PCA) = Identifies and extracts important features in a dataset PCA Process = Standardizes the data and finds new principal components Principal Components = Orthogonal variables capturing maximum variance in the data Dimensionality Reduction = Reduces dataset's dimension while preserving variance

### Match the steps of Principle Component Analysis (PCA) with their descriptions:

Step 2: Compute the covariance matrix = Calculate the covariance matrix based on the standardized data to show relationships and variances between pairs of variables. Step 3: Compute the eigenvectors and eigenvalues = Obtain eigenvectors and eigenvalues by decomposing the covariance matrix, where each eigenvector represents a principal component and its corresponding eigenvalue represents the amount of variance explained. Step 4: Select the principal components = Determine the number of principal components to retain based on the amount of variance explained by each principal component, often using a threshold like retaining components that explain a certain percentage of the total variance. Step 5: Project the data onto the new feature space = Project the original data onto the selected principal components to obtain a reduced-dimensional representation by taking the dot product of the data and the selected principal components.

### Match the applications of Principle Component Analysis (PCA) with their descriptions:

Dimensionality reduction = By selecting a subset of principal components, PCA reduces the dimensionality of the dataset, making it easier to visualize and analyze. Data visualization = PCA can be used to visualize high-dimensional data by projecting it onto a lower-dimensional space, typically two or three dimensions. Noise reduction = By keeping only the principal components that capture most of the variance, PCA can remove noise and retain the most informative features. Feature extraction = PCA can be used to extract the most important features from a dataset and discard less relevant or redundant features.

### Match the mathematical operations in PCA with their descriptions:

Calculate the mean = Determine the mean value for each variable in the dataset. Compute the covariance matrix = Calculate the covariance matrix based on the standardized data to show relationships and variances between pairs of variables. Compute eigenvectors and eigenvalues = Obtain eigenvectors and eigenvalues by decomposing the covariance matrix, where each eigenvector represents a principal component and its corresponding eigenvalue represents the amount of variance explained. Select principal components = Determine the number of principal components to retain based on the amount of variance explained by each principal component, often using a threshold like retaining components that explain a certain percentage of the total variance.

### Match the steps in reducing dimensionality using PCA with their descriptions:

Calculate mean for each variable = Determine the mean value for each variable in the dataset. Compute covariance matrix = Calculate the covariance matrix based on the standardized data to show relationships and variances between pairs of variables. Select principal components = Determine the number of principal components to retain based on the amount of variance explained by each principal component, often using a threshold like retaining components that explain a certain percentage of the total variance. Project data onto new feature space = Project the original data onto the selected principal components to obtain a reduced-dimensional representation by taking the dot product of the data and the selected principal components.

### Match PCA applications with their benefits:

Dimensionality reduction = Reduces complexity and makes it easier to visualize and analyze data. Data visualization = Enables representation of high-dimensional data in lower dimensions for easier understanding and interpretation. Noise reduction = Removes irrelevant or less informative features from datasets, leading to cleaner data analysis results. Feature extraction = Identifies and retains essential information while discarding redundant or less relevant features.

## Study Notes

• Classification: involves predicting a categorical label or class that an instance belongs to
• Regression: involves predicting a continuous or numerical value
• Clustering: involves grouping similar instances together
• Dimensionality Reduction: involves reducing the number of features or variables in a dataset

### Dimensionality Reduction Techniques

• Principal Component Analysis (PCA): linear technique that projects high-dimensional data onto a lower-dimensional space
• t-SNE: non-linear technique that preserves local relationships in the data
• Autoencoders: neural networks that learn to compress and reconstruct data

### Steps of Principle Component Analysis (PCA)

• Data Standardization: subtracting the mean and dividing by the standard deviation for each feature
• Covariance Matrix Calculation: computing the covariance between each pair of features
• Eigenvector and Eigenvalue Calculation: solving for the eigenvectors and eigenvalues of the covariance matrix
• Component Selection: selecting the top k eigenvectors corresponding to the k largest eigenvalues
• Transformation: projecting the original data onto the selected eigenvectors

### Applications of Principle Component Analysis (PCA)

• Data Visualization: reducing dimensionality for visualization in lower-dimensional spaces
• Anomaly Detection: identifying outliers and anomalies in the data
• Feature Extraction: selecting the most informative features in a dataset
• Noise Reduction: removing noise and correlations in the data

### Mathematical Operations in PCA

• Eigen Decomposition: decomposing a matrix into eigenvectors and eigenvalues
• Matrix Multiplication: projecting the original data onto the selected eigenvectors
• Orthogonal Projections: projecting data onto a lower-dimensional space

### Steps in Reducing Dimensionality using PCA

• Selecting the Number of Components: choosing the number of dimensions to reduce to
• Computing the Component Scores: projecting the original data onto the selected eigenvectors
• Transforming the Data: converting the original data into the lower-dimensional space

### PCA Applications and Benefits

• Facial Recognition: reducing dimensionality for efficient face recognition
• Benefit: improved computational efficiency
• Gene Expression Analysis: identifying relevant genes in microarray data
• Benefit: improved feature selection and identification of key genes
• Image Compression: reducing dimensionality for efficient image compression
• Benefit: improved storage and transmission efficiency

This quiz covers the fundamentals of supervised and unsupervised learning, focusing on the differences between them and the concept of unsupervised tasks such as clustering, anomaly detection, and dimensionality reduction including Principle Component Analysis (PCA).

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