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Questions about linear partial differential equations. Often used in combination with the top-level tag ap.analysis-of-pdes.

2 votes

Explicit solutions for linear system of PDEs with constant coefficients

ADDDED: Since equation (1) below is a first order linear ODE,it has an explicit solution (with an integral). It follows that the solution to the entire system of equations can be written explicitly as …
Deane Yang's user avatar
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4 votes
Accepted

Existence for an overdetermined system of PDEs

COMMENT: The answer below is just the proof of the Frobenius theorem (https://en.wikipedia.org/wiki/Frobenius_theorem_(differential_topology) applied to this specific case. The arguments below are als …
Deane Yang's user avatar
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6 votes

System of linear pde with non constant coefficients

If you switch the second and third rows of your system, the differential operator is the same as the linearization of equation (4.3) in Existence of elastic deformations with prescribed principal stra …
Deane Yang's user avatar
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8 votes

Fundamental solution of an elliptic PDE in divergence form with non-symmetric matrix

If you assume that the coefficients $a^{ij}$ are smooth functions and let $$b^{ij} = \frac{1}{2}(a^{ij} + a^{ji}),$$ then the PDE can be written as $$ b^{ij}\partial^2_{ij}u + \partial_ia^{ij}\partial …
Deane Yang's user avatar
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14 votes

Moduli space of linear partial differential equations

Hormander showed that there is a generic set of scalar linear PDE's that can be studied using general techniques, known as microlocal analysis. This can be linked to algebraic geometry as follows: Any …
Deane Yang's user avatar
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5 votes

What does the flow of the principal symbol of the differential operator tell us about the PDE?

It goes something like this (I can't promise that what I've written below is completely correct. It is only to help you read the rigorous details in more definitive reference): The initial observatio …
Deane Yang's user avatar
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2 votes

BVPs for elliptic PDOs: When do Green functions ($L^2$ inverses) define pseudo-differential ...

Assuming that $P^{-1}$ is a right inverse and $\Omega$ an open subset of $\mathbb{R}^n$ or an open manifold, then you can proceed as follows: 1) An operator $Q: L^2(\Omega) \rightarrow L^2\Omega$ is …
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7 votes

Uniform bound on the eigenfunctions of the Laplacian

Moser iteration proceeds roughly like this: If the dimension $n$ is greater than $2$ and we assume homogeneous Dirichlet , we can proceed as follows: Using the Sobolev inequality on $\mathbb{R}^n$, $$ …
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5 votes

Classification of PDE

If you are interested in a real scalar linear PDE with constant coefficients, then it has all been worked out, primarily by Ehrenpreis, using the Fourier transform. Unfortunately, I don't know of a de …
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