Famous Theorems of Mathematics/Applied Mathematics

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-div is adjoint to d[edit]

The claim is made that −div is adjoint to d:

Proof of the above statement:

If f has compact support, then the last integral vanishes, and we have the desired result.

Laplace-de Rham operator[edit]

One may prove that the Laplace-de Rahm operator is equivalent to the definition of the Laplace-Beltrami operator, when acting on a scalar function f. This proof reads as:

where ω is the volume form and ε is the completely antisymmetric Levi-Civita symbol. Note that in the above, the italic lower-case index i is a single index, whereas the upper-case Roman J stands for all of the remaining (n-1) indices. Notice that the Laplace-de Rham operator is actually minus the Laplace-Beltrami operator; this minus sign follows from the conventional definition of the properties of the codifferential. Unfortunately, Δ is used to denote both; reader beware.


Given scalar functions f and h, and a real number a, the Laplacian has the property:


where f and h are scalar functions.