# Questions tagged [differential-equations]

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### The original Dirac equation

In the original 1928 paper (pdf) the Dirac equation appears on page 615 in equation (9) as $$[p_0+\rho_1\left(\boldsymbol{\sigma},\boldsymbol{p}\right)+\rho_3mc]\psi=0\qquad(1)$$ Using the ...
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### Who first used exponential function as a solution of second order differential equations? [duplicate]

You can refer this question from math SE which explains why exponential function is used as a solution of second order differential equations. However, I am interested to know who was the ...
386 views

### Notations for Laplacian: $\nabla^2$ vs. $\Delta$

For a (sufficiently smooth) function $f\colon \Bbb R^n\to\Bbb R$, the Laplacian of $f$ is defined to be $\sum_{j=1}^n \frac{\partial^2 f}{\partial x_j^2}$. There are two notations for the Laplacian ...
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### What does the Fourier transform have to do with heat?

For example the current version of the Fourier analysis article on Wikipedia says the study is: […] named after Joseph Fourier, who showed that representing a function as a sum of trigonometric ...
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### What is the origin of the "Japanese bracket"?

In discussions of Sobolev spaces one often sees the Japanese bracket, $$\langle x \rangle = (1+|x|^2)^{1/2},$$ as useful shorthand. I was not easily able to find information about this term. (1) What ...
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### History behind the heat equation

Who was the first mathematician/physicist to derive the heat equation $u_t=\Delta u$ and when? Was it already known to explain most diffusion phenomena? How much time passed between the first ...
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### What is the etymology of "phase space" of a dynamical system?

The state space of a dynamical system is often called a "phase space". What is the etymology of this? (Note that I'm not asking about the history of the concept, but rather about the history of the ...
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### What kinds of differential equations were solved on the early differential analyzer?

Harold Locke Hazen and Vannevar Bush created the Differential Analyzer at MIT between 1928 and 1931 to solve differential equations, according to the Wikipedia Article on the topic. I've read this ...
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### Who is Wanner from Rosenrock-Wanner (ROW) methods?

I've spent some time with a search engine trying to find out about Wanner, a person whose surname is mentioned in the name of Rosenbrock-Wanner (ROW) methods primarily used for iteratively solving ...
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### From where the so-named "elastica problem" is coming from?

In a book by Cash et al, I see the mention of the so-called Elastica problem (pg 221 in the link here). The problem is presented as a system of ODEs, $$x' = \cos (\phi)$$ $$y' = \sin (\phi)$$...
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### Asymptotically Periodic Potentials

Who came up with the idea of solving elliptic equations with periodic potentials and from there solving elliptic equations with asymptotically periodic potentials? I heard it was Pierre Louis Lions, ...
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### Why was Indicial equations named so?

In ODE, in Frobenius method, there's an equation called "Indicial Equation." Is there any particular contextual/historical reason that it is named so?
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### Source of claim that Leibniz discovered separation of variables for ODEs in 1691?

Claims I'm evaluating I've read in multiple sources that Leibniz formulated separation of variables for ODEs in 1691. A couple example sources are below. Mathematical Thought from Ancient to Modern ...
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### Does the “O” in the google doodle for Olga Ladyzhenskaya have anything to do with her work?

Ladyzhenskaya is famous for fluid dynamics and partial differential equations, both of which are beyond my pay grade. And she worked on the Navier-Stokes equations. Does this circle with the arrows ...
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### Earliest Instances of a Slope/Direction Field for a First-Order ODE

Background When first encountering slope fields in calculus or elementary differential equations, students often ask "What is the purpose?" A concise answer is that slope fields provide a way to ...
233 views

### How did Peano prove his existence theorem without Ascoli's theorem?

In modern proofs of the Peano Existence Theorem for ordinary differential equations, Ascoli's theorem is used. Ascoli's theorem came after Peano's proof. Did Peano prove a form of Ascoli's theorem in ...
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1 vote
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### Why are partial derivatives necessary when deriving the equation for a vibrating string?

AFAIK, partial derivatives made it to the forefront as a result of coming up with an equation for a vibrating string i.e., 1D wave equation. From purely a physical phenomena to math mapping POV: Why ...
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### History of hypergeometric equation

It is known that Gauss studied hypergeometric equation $$x(1-x) \dfrac {d^2y}{dx^2}+(c-(a+b+1)x)\dfrac {dy}{dx}-aby=0$$ I would like to know something about history of this equation: 1) If $a=b=c=0$...
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### What were the early uses of differential equations for modeling chemical reactions?

What are some of the original examples of uses of differential equations for modeling and analyzing chemical reactions, particularly those relevant to biochemistry, involving proteins and enzymes? ...
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### D'Alembertian symbol $\Box$

The D'Alembertian is a generalization of the Laplacian operator to a space of arbitrary dimension and metric. Where does the D'Alembertian symbol $\Box$ come from? According to Wikipedia it has to ...
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### The Original Proofs of The Stable Manifold Theorem

The book "Differential Equations and Dynamical Systems" by Lawrence Perko says that the first proofs of the Stable Manifold Theorem are from Hadamard in 1901, Perron in 1928, and Liapunov and Perron. ...
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1 vote
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### History of PDE's in the 19th Century (part 2)

This is a follow up to this question: History of PDE's in the 19th Century The question I have been given to answer is: The history of partial differential equations in the 19th Century belongs ...
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### History of PDE's in the 19th Century

I've been asked to write an essay on whether the work on PDE's in the 19th century belonged to applied or pure mathematics. Does anyone know of any useful sources I could use?
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### How did Newton write his equations?

Once, after a lecture, my professor of differential equations said, that Newton did not use derivatives in his work as we do today. He told us that Newton rather used some series expansions for his ...
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### Origin of the terminology “trace operator” related to boundary-value problems for PDEs

Important results in the theory of PDEs regarding boundary-value problems are trace and extension theorems. Since the trace operator (not to be confused with the trace from linear algebra) essentially ...
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### Invariance principle for stability in the sense of Lyapunov

On Wikipedia this article about the invariance principle and article states that The general result was independently discovered by J.P. LaSalle (then at RIAS) and N.N. Krasovskii, who published ...
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### Who came up with the link between the spectrum of an operator and the poles of a meromorphic function?

From Dieudonné's "History of Functional Analysis" I learned that Picard in 1893 gave a characterization of an eigenvalue of the Laplacian as the simple pole of a meromorphic function. Is there an ...
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### source of "logistic growth"?

I've been trying to find the source of the name of the DE modelling population growth known as logistic growth, for some time: why "Logistic" ? So far all my attempts to research it have hit dead ends ...
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### Poincare's last geometric theorem

Which problem in celestial mechanics led Poincare to his conjecture about fixed points of area preserving maps of the annulus to itself? I believe he was working on some differential equations. What ...
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### Did Newton find the trajectory of a body moving in uniform gravity under the quadratic resistance law (the ballistic problem)?

I'm very confused by contradicting accounts of a supposed solution by Newton to the problem of finding the trajectory of a projectile moving under uniform gravity against resistance that is ...
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### What is the origin of the term "Ordinary Differential Equation"?

Who first used the term "Ordinary Differential Equation (ODE)"? Is it known why the word "ordinary" is used here? What makes an ODE "ordinary"?
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### Who did first use the Method of Characteristics?

Which mathematician did introduce the Method of Characteristics for solving linear Partial differential equations? I some papers I saw that Saint Venant, Lagrange, Cauchy or Riemann were attributed ...
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### Who invented the exponential ansatz for linear differential equations with constant coefficients?

Who invented using $e^{\lambda t}$ as ansatz for solving linear differential equations with constant coefficients?
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