ML

Statistical, ML and Neural Models of POS Tagging

Statistical, ML and Neural Models of POS Tagging #

‘HMM Inference: Forward and Viterbi Algorithms’ covers the portion:

  • Forward Algorithm
  • Viterbi Algorithm
  • HMM inference for POS tagging

The complete Topic also includes:

  • Maximum Entropy Markov Models
  • Bidirectionality
  • Neural-network models for POS tagging

HMM Inference: Forward and Viterbi Algorithms #

Hidden Markov Models create two closely related inference problems:

  • Likelihood: How probable is an observed sequence under the model?
  • Decoding: Which hidden-state sequence most probably generated the observations?

The Forward Algorithm solves the likelihood problem, while the Viterbi Algorithm solves the decoding problem. Both use dynamic programming and a trellis, but they combine paths differently.

Bayesian Learning

Bayesian Learning #

Bayesian Learning is a probabilistic approach to machine learning.

Instead of only asking, “Which output should the model predict?”, Bayesian Learning asks:

Given the data we have observed, how likely is each hypothesis, class, or parameter value?

This makes Bayesian Learning useful when uncertainty matters.

It is especially important in classification, probabilistic modelling, generative models, and situations where we want to combine prior knowledge with observed data.

Ensemble Learning

Ensemble Learning #

Ensemble Learning is a machine learning approach where we combine multiple models to produce a stronger final prediction.

Instead of depending on one model, an ensemble uses a group of models and combines their outputs.

The main idea is simple:

Many weak or moderately good models can work together to produce a better and more stable model.

Key takeaway:
Ensemble Learning improves prediction by combining several models.

ML System Optimisation

ML System Optimisation #

ML System Optimisation studies how to make machine learning workloads faster, more scalable, more memory-efficient, and suitable for different hardware platforms.

The subject connects machine learning algorithms with the systems that train and deploy them: multi-core CPUs, GPUs, distributed clusters, cloud platforms, edge devices, and embedded systems.

ML system optimisation = model quality + computational efficiency + hardware awareness + scalability

The learning path begins with performance measurement and parallel computing, progresses through distributed machine learning and scale-out platforms, and concludes with model compression and resource-constrained deployment.

Unsupervised Learning

Unsupervised Learning #

Unsupervised Learning is used when we have input data but no target labels.

The model is not told the correct answer. Instead, it tries to discover hidden structure in the data.

  • K-means Clustering and variants
  • Review of EM algorithm
  • GMM based Soft Clustering
  • Applications

Supervised vs Unsupervised Learning #

AspectSupervised LearningUnsupervised Learning
Data contains target label?YesNo
Learns fromInput-output pairsInput features only
Main goalPredict outputDiscover structure
Example taskClassification, regressionClustering
Example algorithmLogistic regression, decision treeK-means, GMM

  • Works on unlabelled raw data.
  • The algorithm discovers hidden patterns without prior knowledge of outcomes.
  • Requires no human intervention during training.
  • Does not make direct predictions — it groups or organises data instead.
  • Carries a higher risk because there’s no ground truth to verify results.
  • Common techniques include Clustering, Association, and Dimensionality Reduction.

The most common example is clustering, where similar records are grouped together.

Linear Algebra

Linear Algebra #

The study of vectors and matrices is called Linear Algebra.

Linear Algebra provides the mathematical language used to represent data, transformations, and structure in ML.


Why Linear Algebra Matters in ML #

  • Every machine learning model uses matrices
  • All data in ML is represented using vectors and matrices
  • Neural networks are pipelines of matrix operations
  • Models apply matrix transformations to data
  • Optimisation relies on linear algebra operations

What to Learn #

  • Scalars, vectors, and matrices
  • Vector operations (addition, dot product)
  • Matrix multiplication (critical)
  • Identity matrices and transpose
  • Eigenvalues and eigenvectors (conceptual understanding)

  • Scalar → a number
  • Vector → a directed point
  • Matrix → a space transformer
  • Linear transformation → structured mapping
  • Feature → one axis
  • Feature space → where data lives
  • Vector space → where vectors live

Home | Mathematical Foundation

Linear Systems

Linear Systems #

How systems of linear equations are represented and solved using matrices.

  • the study of vectors and rules to manipulate vectors
  • describe multiple linear equations solved simultaneously
  • connect algebraic equations with matrix representations

Matrix


Idea of Closure #

  • performing a specific operation (like addition or multiplication) on members of a set always produces a result that belongs to the same set

  • idea of closure is fundamental to defining a Vector space because it ensures that performing arithmetic operations (addition and scalar multiplication) on vectors within a set does not produce a new element outside that set.

Systems of Linear Equations

Systems of Linear Equations #

A system of linear equations can be written compactly as:

\[ A\mathbf{x}=\mathbf{b} \]

This represents:

  • a linear transformation applied to an unknown vector (\mathbf{x})
  • producing an output vector (\mathbf{b})

Key components #

Coefficient matrix (A) #

(A) contains the coefficients of the variables.

Calculus

Calculus #

Calculus is:

  • the mathematical framework for understanding and controlling how quantities change
  • the mathematics of change and accumulation

It helps answer:

  • How fast is something changing right now?
  • What happens when inputs change slightly?
  • Where is something maximum or minimum?

It answers two big questions:

  • How fast is something changing right now? → derivatives (differentiation)
  • How much has accumulated over an interval? → integrals (integration)

flowchart TD
  A[Calculus] --> B[Limits]
  B --> C[Continuity]
  B --> D[Derivatives]
  B --> E[Integrals]
  D --> F[Optimisation: maxima/minima]
  D --> G[ML: gradients & learning]
  E --> H[Accumulation: area/total change]


  1. Differential Calculus (Rates of Change) #

    Studies how things change.