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Referring to the discretization of derivatives by Finite differences, and its applications to numerical solutions of partial differential equations.

4 votes
Accepted

Solve eigenvalue problem using finite differences without vectorization

For sure it is possible with iterative methods, because you can apply your operator $u\mapsto Au$ cheaply while keeping $u$ in "matrix form". It is simply a double nested for cycle. Check out ARPACK, …
Federico Poloni's user avatar
5 votes

Howo to implement complex step derivative for complex functions?

I'm afraid the method only works to compute derivatives of real-valued functions (of which you happen to have an implementation that also works on complex values).
Federico Poloni's user avatar
3 votes

Factorize laplacian in terms of first derivative matrix

@lightxbulb's answer gives the correct factorization already, but since you mention failed attempts with the Cholesky factorization, let me describe a method to discover the factorization numerically, …
Federico Poloni's user avatar
1 vote

How to reorder variables to produce a banded matrix of minimum bandwidth?

While all the present answers are valid solutions to the practical problem, technically the answer to the question in your title (how to reorder variable to minimize bandwidth) is "it's an NP-complete …
Federico Poloni's user avatar
6 votes

Eigenvectors of Laplacian

They're on Wikipedia, for instance, in a page with the slightly unclear name of "Eigenvalues and eigenvectors of the second derivative".
Federico Poloni's user avatar