Deep learning is often taught through libraries, architectures, and ready-to-use models. But behind every neural network are mathematical ideas involving approximation, optimization, probability, analysis, and numerical methods.
Mathematical Introduction to Deep Learning: Methods, Implementations, and Theory by Arnulf Jentzen, Benno Kuckuck, and Philippe von Wurstemberger takes a deeper approach. The book combines mathematical theory with implementations and practical code, making it useful for readers who want to understand not only how deep learning works, but also the mathematical reasoning behind its algorithms.
The work was first submitted to arXiv in 2023 and the current arXiv version is v3, revised July 15, 2025. The current version contains 737 pages, 33 figures, 45 source codes, and 87 exercises.
Download the PDF for free: https://arxiv.org/pdf/2310.20360
What Is This Book About?
The main goal of the book is to provide a mathematical introduction to deep learning algorithms.
It covers three important dimensions:
Methods — different neural network architectures and learning algorithms
Implementations — practical Python source code
Theory — mathematical analysis of approximation, optimization, and generalization
The authors explicitly state that the resource is intended both for students and scientists who are new to deep learning and for practitioners who want a stronger mathematical understanding of the methods they already use.
Artificial Neural Networks
The book begins with the fundamental building blocks of artificial neural networks.
Readers study how neural networks represent functions and how different components work together to transform input information into predictions.
The discussion includes several important architectures:
Fully connected feedforward networks
Convolutional neural networks
Recurrent neural networks
Residual neural networks
Networks using batch normalization
Rather than treating these architectures as black-box components from a library, the book examines their mathematical structure in detail.
Activation Functions
Activation functions play an important role in neural networks because they allow networks to represent complex relationships.
The book examines activation functions from a mathematical perspective and connects them to the ability of neural networks to approximate functions.
This is an important difference from introductory deep learning tutorials, where activation functions are often introduced mainly as practical choices.
Here, the reader is encouraged to understand why these functions matter mathematically.
Neural Network Calculus
One particularly interesting aspect of the book is its treatment of calculus for neural networks.
The authors investigate how mathematical analysis can be applied to neural-network architectures and their components.
This provides a foundation for understanding:
Differentiation
Gradients
Optimization
Backpropagation
Sensitivity of models
Training behavior
The goal is to connect familiar deep learning operations with the mathematical principles underneath them.
Approximation Theory
A major theoretical theme is approximation.
Neural networks are powerful because they can approximate complicated relationships between inputs and outputs.
The book studies the approximation capabilities of neural networks in mathematical detail. It asks questions such as:
What kinds of functions can neural networks represent?
How accurately can they approximate complicated functions?
How does network architecture affect approximation?
These questions are fundamental to understanding why neural networks can be so expressive.
Optimization and Training
Training a deep learning model is essentially an optimization problem.
The book therefore spends substantial attention on optimization methods used to train neural networks.
Topics include:
Gradient-based optimization
Stochastic gradient descent
Accelerated optimization methods
Adaptive optimization methods
Optimization theory
Convergence-related questions
The current version specifically notes that Chapters 5, 6, and 7 in the optimization section were expanded in version 3.
This makes the optimization section particularly valuable for readers who want to understand what happens during neural-network training rather than simply calling an optimizer from a framework.
Stochastic Gradient Descent
Stochastic gradient descent is one of the fundamental optimization methods in deep learning.
The book examines it from both an algorithmic and mathematical perspective.
Instead of simply saying that an optimizer "updates the weights," the theoretical treatment explores why these updates can lead toward useful solutions and what mathematical properties influence the optimization process.
This is especially helpful for advanced learners who want to move from using optimization algorithms to understanding them.
Adaptive and Accelerated Methods
The book also discusses optimization methods that attempt to improve the training process.
These approaches can modify how optimization progresses based on information obtained during training.
Studying these methods mathematically helps readers understand why different optimization strategies can behave differently when training neural networks.
Generalization
Another central topic is generalization.
A neural network can perform extremely well on training data while behaving differently on previously unseen data.
The book investigates the mathematical theory behind generalization errors.
This connects deep learning with broader ideas from statistical learning and probability.
Understanding generalization is important because successful machine learning is not simply about memorizing training examples. A useful model needs to capture patterns that transfer to new data.
Optimization Theory
The book goes deeper into optimization theory than most practical deep learning tutorials.
One of the advanced topics mentioned by the authors is the Kurdyka–Łojasiewicz inequality, which is used in mathematical analysis related to optimization.
This makes the resource particularly interesting for readers with backgrounds in mathematics, applied mathematics, or theoretical machine learning.
Deep Learning and Partial Differential Equations
The final part of the book moves beyond conventional machine learning applications and connects deep learning with partial differential equations (PDEs).
This is an important bridge between deep learning and scientific computing.
The book reviews deep learning approximation methods for PDEs, including:
Physics-Informed Neural Networks
Deep Galerkin methods
These approaches demonstrate how neural networks can be used to approximate solutions to scientific and mathematical problems.
Physics-Informed Neural Networks
Physics-Informed Neural Networks, commonly called PINNs, combine neural networks with information derived from physical or mathematical constraints.
Instead of learning only from conventional datasets, the model can incorporate knowledge about the underlying system.
This makes PINNs interesting for areas such as:
Computational physics
Engineering
Scientific computing
Differential equations
Simulation
The inclusion of PINNs gives the book a useful connection between theoretical deep learning and scientific machine learning.
Deep Galerkin Methods
The book also discusses Deep Galerkin methods, another approach for using neural networks to approximate solutions to differential-equation problems.
This demonstrates the broader role that neural networks can play beyond conventional classification and regression tasks.
Deep learning becomes a computational tool for mathematical modeling rather than only a predictive technique.
Practical Implementations
Despite its mathematical focus, the book is not purely theoretical.
The current arXiv version lists 45 source codes, and a companion GitHub repository contains the Python code associated with the book.
This combination of theory and implementation is one of the strongest aspects of the resource.
Readers can study a concept mathematically and then examine how the corresponding idea can be implemented computationally.
Python and Coding
The companion repository describes itself as containing all of the Python code from the book.
For Python and deep learning learners, this provides a useful bridge:
Mathematical concept → Algorithm → Python implementation
That structure can help readers connect theoretical knowledge with practical programming.
Exercises
The current version contains 87 exercises, providing opportunities to work through the concepts rather than simply reading them.
For a mathematical subject like deep learning theory, exercises are particularly important because many concepts become clearer only after the reader attempts to apply them independently.
Why This Book Matters for AI and Deep Learning
Modern deep learning is often approached through frameworks such as PyTorch and TensorFlow.
These tools make it possible to build powerful models without requiring users to understand every mathematical detail.
However, this can also create a gap between using a model and understanding the model.
This book attempts to reduce that gap.
It connects:
Mathematics → Deep Learning Algorithms → Implementation → Theory
That makes it particularly valuable for readers who want to progress from simply building neural networks toward understanding the foundations behind them.
Who Should Read This Book?
This book is suitable for:
Deep learning students
Mathematics students
Applied mathematics students
Machine learning researchers
AI researchers
Data scientists wanting stronger mathematical foundations
Python developers interested in deep learning theory
Students interested in scientific machine learning
Beginners can use it as a foundation, but readers should expect a significantly more mathematical treatment than a typical practical deep learning tutorial.
Strengths
1. Strong Mathematical Foundation
The book explains deep learning through mathematical analysis rather than treating neural networks as black boxes.
2. Theory + Implementation
The combination of theoretical discussion and Python source code makes the material more practical.
3. Wide Coverage
It covers neural-network architectures, optimization, approximation theory, generalization, and PDE applications.
4. Useful for Advanced Learners
Readers interested in theoretical machine learning can use it to explore topics that are often skipped in application-focused courses.
5. Openly Available
The work is available as an arXiv preprint, making the current version freely accessible online.
Limitations
The biggest limitation is also one of its strengths: the mathematical depth.
Someone looking for a quick introduction to building neural networks with PyTorch may find the material considerably more theoretical than expected.
It is better suited to readers who are willing to spend time understanding mathematical reasoning, optimization, approximation, and analysis.
It should therefore be viewed less as a quick-start deep learning cookbook and more as a deep mathematical foundation for deep learning.
Download the PDF for free: https://arxiv.org/pdf/2310.20360
Final Verdict
Mathematical Introduction to Deep Learning: Methods, Implementations, and Theory provides a detailed bridge between mathematics and modern deep learning.
Instead of focusing only on how to train models, it explores the mathematical structures behind neural networks, their approximation capabilities, optimization algorithms, generalization, and scientific applications.

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