
What Exactly is Dirac’s Delta Function?
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Introduction: "Convenient Notation"In Dirac's Principles of Quantum Mechanics published in 1930 he introduced a "convenient notation" he referred …

Fixing Things Which Can Go Wrong With Complex Numbers
Abstract
This article will build on the hints about treating the complex numbers as a branched surface, briefly described and pictured in section 4.2…

Series in Mathematics: From Zeno to Quantum Theory
Introduction
Series play a decisive role in many branches of mathematics. They accompanied mathematical developments from Zeno of Elea (##5##-th century…

Epsilontic – Limits and Continuity
Abstract
I remember that I had some difficulties moving from school mathematics to university mathematics. From what I read on PF through the years, I…

Differential Equation Systems and Nature
Abstract
"Mathematics is the native language of nature." is a phrase that is often used when it comes to explaining why mathematics is all around in natural…

Beginners Guide to Precalculus, Calculus and Infinitesimals
Introduction
I am convinced students learn Calculus far too late. In my view, there has never been a good reason for this.In the US, they go through…

What Are Numbers?
Introduction
When doing mathematics, we usually take for granted what natural numbers, integers, and rationals are. They are pretty intuitive. Going…

What Are Infinitesimals – Simple Version
Introduction
When I learned calculus, the intuitive idea of infinitesimal was used. These are real numbers so small that, for all practical purposes (say…

What Are Infinitesimals – Advanced Version
Introduction
When I learned calculus, the intuitive idea of infinitesimal was used. These are real numbers so small that, for all practical purposes (say…

The Art of Integration
Abstract
My school teacher used to say
"Everybody can differentiate, but it takes an artist to integrate."
The mathematical reason behind this phrase…

An Overview of Complex Differentiation and Integration
Abstract
I want to shed some light on complex analysis without getting all the technical details in the way which are necessary for the precise treatments…

Reduction of Order For Recursions
This is not meant as a full introduction to recursion relations but it should suffice for just about any level of the student.Most of us remember recursion…

A Novel Technique of Calculating Unit Hypercube Integrals
Introduction
In this insight article, we will build all the machinery necessary to evaluate unit hypercube integrals by a novel technique. We will first…

The Amazing Relationship Between Integration And Euler’s Number
We use integration to measure lengths, areas, or volumes. This is a geometrical interpretation, but we want to examine an analytical interpretation that…

How to Solve Second-Order Partial Derivatives
Introduction
A frequent concern among students is how to carry out higher order partial derivatives where a change of variables and the chain rule are…

The Orin Fractional Calculus
Introduction
This bit is what new thing you can learn reading this:) As for original content, I only have hope that the method of using the sets
$$C_N^n:…

How to Find a Potential Function of a Vector Field
Definition and summary
Given a vector field ##\vec F(x,y,z)## that has a potential function, how do you find it?
Conditions and equations
$$\nabla \phi(x,y,z)…

Real Numbers: Definition, Properties & Completeness
Definition of real numbers
Real numbers are the set of all values that can appear on the continuous number line. They include rational numbers (fractions…

What is Integration By Parts? A 5 Minute Introduction
Definition/Summary
In this article, we shall learn a method for integrating the product of two functions. This method is derived from the 'product rule'…

Limits of Functions for Calculus: Definition & Examples
What is a limit?
In mathematics, a limit describes the behavior of a function or sequence as its input approaches a particular value. Limits are a cornerstone…

Demystifying Parameterization and Surface Integrals
Introduction
This article will attempt to take the mystery out of setting up surface integrals. It will explain the basic ideas underlying surface integration…

A Numerical Insight for the Fundamental Theorem of Calculus
The purpose of this article is not to provide some rigorous statement, neither a rigorous clever proof of the fundamental theorem of calculus. It is rather…

Learn the Basics of Hilbert Spaces and Their Relatives: Operators
Operators. The Maze Of Definitions.
We will use the conventions of part I (Basics), which are ##\mathbb{F}\in \{\mathbb{R},\mathbb{C}\}##,…

Learn the Basics of Hilbert Spaces and Their Relatives: Definitions
Basics
Language first: There is no such thing as the Hilbert space.Hilbert spaces can look rather different, and which one is used in…

Demystifying the Chain Rule in Calculus
Introduction
There are a number of posts on PF involving a general confusion over the multi-variable chain rule. The problem is often caused by…

Learn Further Sums Found Through Fourier Series
In an earlier insight, I looked at the Fourier series for some simple polynomials and what we could deduce from those series. There is a lot more to be…

Learn an Integral Result from Parseval’s Theorem
Introduction:
In this Insight article, Parseval's theorem will be applied to a sinusoidal signal that lasts a finite period of time. It will be shown…

The Pantheon of Derivatives – Important Theorems (V)
Implicit Function Theorem [1]
Jacobi Matrix (Chain Rule).
Let ## (x_0,y_0 ) ## be a point in$$U_1 \times U_2 = \{x \in \mathbb{R}^k\,\vert \,||x-x_0||<…

The Pantheon of Derivatives – Manifolds And Vector Fields (II)
Generalizations Beyond ##\mathbb{R}## and ##\mathbb{C}##
As mentioned in the section on complex functions (The Pantheon of Derivatives - Part…

The Pantheon of Derivatives – The Direction (I)
Differentiation in a Nutshell
I want to gather the various concepts in one place, to reveal the similarities between them, as they are often…

Trick to Solving Integrals Involving Tangent and Secant
This little trick is used for some integration problems involving trigonometric functions is probably well-known, but I only learned it yesterday. So…

Using the Fourier Series To Find Some Interesting Sums
Preliminaries
If f(x) is periodic with period 2p and f’(x) exists and is finite for -π<x<π, then f can be written as a Fourier series:
[itex]f(x)=\sum_{n=-\infty}^{\infty}a_{n}e^{inx}…

Learn Partial Differentiation Without Tears
Differentiation is usually taught quite well. Perhaps that's because it is the first introduction to calculus, which is considered a big step in a student's…

Why the Gauge (Henstock-Kurzweil) Integral Matters
The gauge integral (Henstock–Kurzweil)
The current (pure) mathematics curriculum at the university is well-established. Most of the choices made are…

Integration Paradoxes: Indefinite Integrals and Constants
Introduction
Integration is an incredibly useful technique taught in all calculus classes. Nevertheless, there are certain paradoxes involved with integration…

Advanced Real Analysis: Measure & Functional Study Plan
Prerequisites
If you wish to follow this guide, you should be familiar with analysis on ##\mathbb{R}## and ##\mathbb{R}^n##. See my previous insight for…

Self-Study Analysis Roadmap: From Proofs to Manifolds
Introduction
This is a sequel to my posts on self-studying mathematics. I have already given a very detailed road map on how to study high school mathematics…

Hear the Case for Learning Complex Math
Resistance to complex math seems to never die out. I see it frequently in PF posts. Often it takes the form of challenges rather than questions. …

Things Which Can Go Wrong with Complex Numbers
At the first sight, there are many paradoxes in complex number theory. Here are some nice examples of things that don't seem to work:Example A
[itex]-1=i^2=\sqrt{-1}\cdot\sqrt{-1}=\sqrt{(-1)(-1)}=\sqrt{1}=1[/itex]Example…

How to Solve Nonhomogeneous Linear ODEs using Annihilators
My previous Insights article, Solving Homogeneous Linear ODEs using Annihilators, discussed several examples of homogeneous differential equations, equations…

Solving Homogeneous Linear ODEs using Annihilators
In this Insights article we'll look at a limited class of ordinary differential equations -- homogeneous linear ODES with constant coefficients. Although…

Why 1 Equals 0.999… — Explanations & Rigorous Proofs
Why do people say 1 and 0.999... are equal? Aren't they two different numbers?
No — 1 and 0.999... really are the same number, although that can feel…

Mathematical Proofs: How to Understand and Write Them
Introduction
This FAQ is about proofs. Proofs are central to mathematics, and writing proofs is a skill many people find hard to master. There are two…

Informal Introduction to Cardinal Numbers
Cardinal numbers
We will now give an informal introduction to cardinal numbers. We will later formalize this by using ordinal numbers. Informally, cardinal…

Infinity in Mathematics: Limits and Cardinality FAQ
Introduction
Understanding the behavior of infinity is one of the major accomplishments of mathematics. However, the infinite is often misunderstood and…

Rigorous Proof: Why 0.999… Equals 1 (Geometric Series)
Yes.
What 0.999... Means
First, we have not addressed what 0.999... means. So it is best to first describe what the notation [tex]b_0.b_1b_2b_3...[/tex]…

Nowhere Differentiable Functions: Fejér Kernel & Cesàro Sums
This is Part 2 of a series of articles in which the goal is to exhibit a continuous function that is nowhere differentiable and to explore some interesting…

Constructing a Continuous but Nowhere Differentiable Function
When studying calculus, we learn that every differentiable function is continuous, but a continuous function need not be differentiable at every point.…
