What is Partial differential equations: Definition and 137 Discussions
In mathematics, a partial differential equation (PDE) is an equation which imposes relations between the various partial derivatives of a multivariable function.
The function is often thought of as an "unknown" to be solved for, similarly to how x is thought of as an unknown number, to be solved for, in an algebraic equation like x2 − 3x + 2 = 0. However, it is usually impossible to write down explicit formulas for solutions of partial differential equations. There is, correspondingly, a vast amount of modern mathematical and scientific research on methods to numerically approximate solutions of certain partial differential equations using computers. Partial differential equations also occupy a large sector of pure mathematical research, in which the usual questions are, broadly speaking, on the identification of general qualitative features of solutions of various partial differential equations. Among the many open questions are the existence and smoothness of solutions to the Navier–Stokes equations, named as one of the Millennium Prize Problems in 2000.
Partial differential equations are ubiquitous in mathematically-oriented scientific fields, such as physics and engineering. For instance, they are foundational in the modern scientific understanding of sound, heat, diffusion, electrostatics, electrodynamics, fluid dynamics, elasticity, general relativity, and quantum mechanics. They also arise from many purely mathematical considerations, such as differential geometry and the calculus of variations; among other notable applications, they are the fundamental tool in the proof of the Poincaré conjecture from geometric topology.
Partly due to this variety of sources, there is a wide spectrum of different types of partial differential equations, and methods have been developed for dealing with many of the individual equations which arise. As such, it is usually acknowledged that there is no "general theory" of partial differential equations, with specialist knowledge being somewhat divided between several essentially distinct subfields.Ordinary differential equations form a subclass of partial differential equations, corresponding to functions of a single variable. Stochastic partial differential equations and nonlocal equations are, as of 2020, particularly widely studied extensions of the "PDE" notion. More classical topics, on which there is still much active research, include elliptic and parabolic partial differential equations, fluid mechanics, Boltzmann equations, and dispersive partial differential equations.
To find a shock wave, do we always solve the equation ##x_{\xi}=0##? The PDEs I consider are of the form ##u_t + g(u) u_x = f(u)##, with initial condition ##u(x,0) = h(x)##. I have been looking at the solutions for problems in my homework sheet but this method was used with no explanation.
Why...
I woud like to find the characteristic curves for ##u_t + (1-2u)u_x = -1/4, u(x,0) = f(x)## where ##f(x) = \begin{cases} \frac{1}{4} & x > 0 \\ \frac{3}{4} & x < 0 \end{cases}##.
By using the method of chacteristics, I obtain the Charpit-Lagrange system of ODEs: ##dt/ds = 1##, ##dx/ds = 1 -...
Some may say that ##\frac{ \partial g }{ \partial t }## is correct because it is a term in a partial differential equation, but since ##g## is a one variable function with ##t## only, I think ##\frac{ dg }{ dt }## is correct according to the original usage of the derivative and partial...
using the equation ##u(x,y)=f(x)g(y)##, first, I substitute the value of ##u_{xx}## and ##u_{yy}## in the given PDE. after that solve the ODEs but I can't understand about the ##u_{t}##.In my solution, I put ##u_{t}=0## because u is only the function of x and y. Is it the right approach, to me...
I want to model the advection of debris rock layer with a thickness hd on top of a glacier through ice flow with velocity components u and v. Can anybody explain the physical difference between these 2 equations and which one I should take? Thanks
I am going through this page again...just out of curiosity, how did they arrive at the given transforms?, ...i think i get it...very confusing...
in general,
##U_{xx} = ξ_{xx} =ξ_{x}ξ_{x}= ξ^2_{x}## . Also we may have
##U_{xy} =ξ_{xy} =ξ_{x}ξ_{y}.## the other transforms follow in a similar manner.
I am reading on this part; and i realize that i get confused with the 'lettering' used... i will use my own approach because in that way i am able to work on the pde's at ease and most importantly i understand the concept on separation of variables and therefore would not want to keep on second...
As human beings, we tend to act and observe and think over time periods spanning a few milliseconds to several decades (or even centuries.) Essentially all phenomena that we directly engage with in everyday life are electrodynamical (with quantum electrodynamics over reasonably short time and...
I have tried to Fourier transform in ##x## and get the result in the transformed coordinates, please check my result:
$$
\tilde{u}(k, y) = \frac{1-e^{-ik}}{ik}e^{-ky}
$$
However, I'm having some problems with the inverse transform:
$$
\frac{1}{2\pi}\int_{-\infty}^\infty...
We know
$$
K(x,t) = \frac{1}{\sqrt{4\pi t}}\exp(-\frac{x^2}{4t})
$$
is a solution to the heat equation:
$$
\frac{\partial u}{\partial t} = \frac{\partial^2 u}{\partial x^2}
$$
I would like to ask how to prove:
$$
u(x,t) = \int_{-\infty}^{\infty} K(x-y,t)f(y)dy
$$
is also the solution to...
Any idea how to solve this equation:
## \ddot \sigma - p e^\sigma - q e^{2\sigma} =0 ##
Or
## \frac{d^2 \sigma}{dt^2} - p e^\sigma - q e^{2\sigma} =0 ##
Where p and q are constants.
Thanks.
I've tried to show b) by using the sine Fourier series on ##[0,2a]##, to get ##g_k = \Sigma_{n=0}^{2a} \sqrt\frac{2}{a} Sin(q_k x)##
Therefore ##\sqrt\frac{2}{a} = \frac{1}{a} \int_0^{2a} Sin(q_kx)g_k dx##
These are equal therefore it is an orthonomal basis.
I'm not sure if this is correct so...
I'm solving the heat equation on a ring of radius ##R##. The ring is parameterised by ##s##, the arc-length from the 3 o'clock position. Using separation of variables I have found the general solution to be:
$$U(s,t) = S(s)T(t) = (A\cos(\lambda s)+B\sin(\lambda s))*\exp(-\lambda^2 kt)$$...
The function should use (r,z,t) variables
The domain is (0,H)
Since U is not dependent on angle, then theta can be ignored in the expression for Laplacian in cylindrical coordinates(?)
Solve the boundary value problem
Given
u_{t}=u_{xx}
u(0, t) = u(\pi ,t)=0
u(x, 0) = f(x)
f(x)=\left\{\begin{matrix}
x; 0 < x < \frac{\pi}{2}\\
\pi-x; \frac{\pi}{2} < x < \pi
\end{matrix}\right.
L is π - 0=π
λ = α2 since 0 and -α lead to trivial solutions
Let
u = XT
X{T}'={X}''T...
I have been struggling with a problem for a long time. I need to solve the second order partial differential equation
$$\frac{1}{G_{zx}}\frac{\partial ^2\phi (x,y)}{\partial^2 y}+\frac{1}{G_{zy}}\frac{\partial ^2\phi (x,y)}{\partial^2 x}=-2 \theta$$
where ##G_{zy}##, ##G_{zx}##, ##\theta##...
I am struggling to figure out how to approach this problem. I've only solved a homogenous heat equation $$u_t = u_{xx}$$ using a Fourier transform, where I can take the Fourier transform of both sides then solve the general solution in Fourier terms then inverse transform. However, since this...
When using the separation of variable for partial differential equations, we assume the solution takes the form u(x,t) = v(x)*g(t).
What is the justification for this?
I am trying to determine an outer boundary condition for the following PDE at ##r=r_m##: $$ \frac{\sigma_I}{r} \frac{\partial}{\partial r} \left(r \frac{\partial z(r,t)}{\partial r} \right)=\rho_D gz(r,t)-p(r,t)-4 \mu_T \frac{\partial^2z(r,t)}{\partial r^2} \frac{\partial z(r,t)}{\partial t} $$...
I've a system of partial diff. eqs. in thermo-elasticity, I can solve it using normal mode analysis method but I need to solve it using laplace or Fourier
Salutations,
I have been trying to approach a modelling case about organism propagation which reproducing with velocity $$\alpha$$ spreading randomly according these equations:
$$\frac{du(x,t)}{dt}=k\frac{d^2u}{dx^2} +\alpha u(x,t)\\\ \\ u(x,0)=\delta(x)\\\ \lim\limits_{x \to \pm\infty}...
While separating variables in the Schrodinger Equation for hydrogen atom, why are we taking separation constant to be l(l+1) instead of just l^2 or -l^2, is it just to make the angular equation in the form of Associated Legendre Equation or is there a deeper meaning to it?
Hello all
I am using the method of lines to solve the following PDE:
## \frac {\partial C} {\partial t} + F\frac {\partial q} {\partial t} + u \frac {dC} {dz} = D_{ax} \frac{\partial^2 C} {\partial z^2} ##
## \frac {\partial q} {\partial t} = k (q^{*}-q) ##
With these initial conditions:
##...
Hi,
I'm attempting to learn differential equations on my own. Does anyone recommended a textbook that comes with/has a solution manual? I learn faster when I can see a problem worked out if I can't solve it.
Thanks.
1. The problem statement, all variables, and given/known data
Given is a second order partial differential equation $$u_{xx} + 2u_{xy} + u_{yy}=0$$ which should be solved with change of variables, namely ##t = x## and ##z = x-y##.
Homework Equations
Chain rule $$\frac{dz}{dx} = \frac{dz}{dy}...
1. The problem statement, all variables, and given/known data
Task requires you to solve a partial differential equation $$u_{xy}=2yu_x$$ for ##u(x,y)##. A hint is given that a partial differential equation can be solved in terms of ordinary differential equations.
According to the solution...
During solution of a PDE I came across following ODE
##
\frac{d \bar h}{dt} + \frac{K}{S_s} \alpha^2 \bar h = -\frac{K}{S_s} \alpha H h_b(t)
##
I have to solve this ODE which I have done using integrating factor using following steps
taking integrating factor I=\exp^{\int \frac{1}{D} \alpha^2...
Homework Statement
Considering the function $$f(x) = e^{-x}, x>0$$ and $$f(-x) = f(x)$$. I am trying to find the Fourier integral representation of f(x).
Homework Equations
$$f(x) = \int_0^\infty \left( A(\alpha)\cos\alpha x +B(\alpha) \sin\alpha x\right) d\alpha$$
$$A(\alpha) =...
In the following question I need to find the Fourier cosine series of the triangular wave formed by extending the function f(x) as a periodic function of period 2
$$f(x) = \begin{cases}
1+x,& -1\leq x \leq 0\\
1-x, & 0\leq x \leq 1\\\end{cases}$$
I just have a few questions then I will be able...
Hello, dear colleague. Now I'm dealing with issues of modeling processes of heat and mass transfer in frozen and thawed soils. I am solving this problems numerically using the finite volume method (do not confuse this method with the finite element method). I found your article: "Numerical...
Sashatgu
Thread
Composite
Composite function
Derivatives
Finite difference method
Function
PartialPartial derivatives
Partialdifferentialequations
Hello everybody.
Consider
$$\frac{\partial}{\partial t}f(x) + ax\frac{\partial }{\partial x}f(x) = b x^2\frac{\partial^2}{\partial x^2}f(x)$$
This is the equation (19) of...
Hi, I need to solve a system of first order partial differential equations with complex variables given by
What software should I use for solving this problem..? The system includes 13 differential equations ...
Hello All,
I would like to convert a partial diff equation in time domain into frequency domain, however there is a term of the form:
Re(∇(E1.E2*) exp(j[ω][/0]t))
where E1 and E2 are the magnitudes of the electric field and [ω][/0] is the angular frequency.
Can someone please help me to...
Hello everybody. I'm about to take a final exam and I've just encountered with this exercise. I know it's simple, but i tried solving it by Separation of variables, but i couldn't reach the result Mathematica gave me. This is the equation:
∂u/∂x = ∂u/∂t
Plus i have a condition...
Homework Statement
Solve ut+3ux=0, where -infinity < x < infinity, t>0, and u(x,0)=f(x).
Homework Equations
Fourier Transform where (U=fourier transform of u)
Convolution Theorem
The Attempt at a Solution
I've used Fourier transform to get that Ut-3iwU=0 and that U=F(w)e3iwt. However, I'm...
Hi all,
I'm currently a second year Applied Maths and Physics student. I will be specialising in Experimental physics next year.
With this, I will have no more core (mandatory) mathematics modules.
So far, I have taken, Linear Algebra I, Calculus, Differential Equations, Linear Algebra II...
Hello everyone. So I wanted to get some opinions on what some of you thought was a better choice, as far taking PDE's or classical mechanics 2 goes. First let me start off by giving a little info; I've already taken calc 1-3 and ordinary differential equations, physics 1 & 2...
ρCp (∂T/∂t) + k (∂2T/∂x2) = exp(-σt2)exp(-λx2)φo
i have this equation... i was thinking of taylor series expansion to solve it and make it easier...
any ideas on how to solve?
Homework Statement
Homework Equations
The Attempt at a Solution
Because we are only looking at a cross section, I tried to reduce 5.3 down to just being a function of R and Theta. However I reasoned that there should be, based on this problem, no dependence on Theta either, so I figured I...
Homework Statement
Graph snapshots of the solution in the x-u plane for various times t if
\begin{align*}
f(x) =
\begin{cases}
& 3, \text{if } -4 \leq x \leq 0 \\
& 2, \text{if } 4 \leq x \leq 8 \\
& 0, \text{otherwise}
\end{cases}
\end{align*}
Homework Equations
Assuming that c=1 and g(x)...
What are some good general textbooks on the properties and solution of systems of partial differential equations? I'm most interested in the general theory of vector and tensor valued PDEs like Maxwell's, Navier-Stokes, and the bulk equations governing elasticity and deformation of solids, etc...
We know that modes of vibration of an Euler-Bernoulli beam are given by eigenfunctions, with the natural frequency of each mode being given by its eigenvalue. Thus these modes are all mutually orthogonal.
Can anything be said of the derivatives of these eigenfunctions? For example, I have the...
I need to solve the well known momentum equation in 3D cylindrical coordinates:
ρ(∂v/∂t +(v.∇)v)=A
where A and the velocity v are both local vector variables.
I am actually looking for the stationary solution to the equation, i.e. no ∂/∂t term)
I have tried evolving the velocity and tried...
I have a PDE which is the following:
$$\frac {\partial n}{\partial t} = -G\cdot\frac {\partial n}{\partial L}$$
with boundary condition: $$n(t,0,p) = \frac {B}{G}$$
, where G is a constant, L is length and t is time.
G and B depend on a set of parameters, something like $$B = k_1\cdot C^a$$...
I'm trying to understand the derivation for methods of Greens functions for PDEs but I can't get my head around some parts. I'm starting to feel comfortable with the method itself but I want to understand why it works.
The thing I have problem with is quite crucial and it is the following:
I...
Homework Statement
I have the solution to the heat equation, with the BC's and everything but the IC applied. So I am just trying to solve for the coefficients, the solution without the coefficients is
$$u(x,t) = \sum_{n=1}^{\infty} A_n\sin(nx)e^{-n^2t}$$
If the initial condition is ##u(x,0) =...