Questions tagged [preconditioning]
For questions regarding design and implementation of preconditioners for solving linear systems.
128
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Difference between explicit and implicit preconditioning
What is the difference between an explicit and implicit preconditioner?
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Accelerating Conjugate Gradients fitting for small localized kernel (like cubic B-spline)
Question:
Is there some pre-conditioner for Conjugate-Gradient (CG) cheap enough, that it is worth using even if my operator is very local (i.e. already has a low number of non-zero elements), as it ...
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Iterative solution of ill-conditioned matrix systems
I want to solve a matrix system of the form $Ax=b$ where $A$ is ill-conditioned. The matrix system comes from a structural simulation problem which was discretized using finite elements. I do not have ...
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Simplest way to precondition Uzawa iteration
I have a diffusion problem with an internal circular dirichlet constraint and a side condition which shall enforce a certain global volume integral.
$\nabla(D \nabla u(x)) = 0$
outer boundary ...
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Computing preconditioner for a non-linear conjugate gradient implementation
Consider the following steps for the $i$-th non-linear conjugate gradient iteration, in the context of 3D electromagnetic inversion, and as discussed in (Newman and Boggs, 2004):
(1) set $i = 1$, ...
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Preconditioning of two step iteration for dense matrices
I would like to solve a dense linear system the form in python
$$
L\left(\boldsymbol{x}\right):=\left[\gamma^+\left[\boldsymbol{A}+\frac{1}{2}\boldsymbol{B}^{-1}\right]
+\gamma^-\left[\boldsymbol{A}-\...
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Bachelor thesis going out of hand, need help [closed]
I am currently working on my bachelor thesis, which aims to enhance the multigrid preconditioned conjugate gradient algorithm proposed by Tatebe in 1993 using Deep Learning.
Currently, I am ...
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preconditioning least square in python?
For a nonsymmetric matrix, we can solve { A^T @ A x = A^T b } by lsqr or cgls or something else. Usually it will be slow, so we need a preconditioner either ilu, multigrid or something else. Is there ...
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Interpreting iterative smoothers and solvers as krylov preconditioners
Various literature and library implementations like petsc use preconditioners based on simple smoothers that themselves could be used the solve the systems directly. e.g. say I have a function
...
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What is the current state of preconditioning highly heterogeneous equations? Where do I start?
Consider the simple standard Laplacian in 2D or 3D:
$$\nabla (\alpha \nabla u) =f $$
with $\alpha$ being a scalar. $\alpha$ can take values that can vary largely between 1e-8 and 1 throughout the ...
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Implementations of the Eisenstat-trick for SSOR
Where can I find a source code for the SSOR method with Eisenstat's trick?
The original paper includes pseudo code but also seems to have minor typos. For that reason, I would be very happy to see an ...
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Hessian-free preconditioner for non linear least squares
I am solving a nonlinear least squares problem using Gauss Newton method. Due to the large dimension of the problem, I use the Hessian-free approach. As a linear solver I use either MINRES or CG. To ...
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Upper bound on condition number in linear preconditioning
I'm studying iterative methods for solving linear system, and I find the following setting in Wikipedia:
Consider a matrix splitting $A = M-N$, where $A,M,N$ are all symmetric and positive definite ...
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Kinetic preconditioning
Publication arXiv:0804.2583 describes a method for doing self-consistent iteration without having to diagonalize the Hamiltonian operator at every step.
IX. PRECONDITIONING
As already mentioned, ...
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Why does PETSc take unexpectedly long to set up its KSP solver with a custom preconditioner? [closed]
I am attempting to solve a large system, $\bf{Ax} = \bf{b}$ with the help of PETSc. Due to the size of the problem, I'm using a matrix-free approach, where $\bf{A}$ is just a shell. I'm also providing ...
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Non-overlaping Domain decomposition - assemble of Laplacian
I am dealing with following 2-dimensional problem in the unit square domain $S_2$
$$- \Delta u (x,y) = f \ \text{in} \ S_2, \hspace{1.5cm} u(x,y) = 0 \ \text{on} \ \partial S_2$$
where $f$ is ...
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Eigenvalue analysis of preconditioned partial differential operator
today, I encountered a confused problem by accident, but I have no ideas to deal with it fully. The question can be described as follows: for example, when we need to use FDM/FEM to discrete the ...
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Where can I find matrices and it's preconditioner for testing?
I want to find some kinds of matrices for testing my code such as GMRES , MINRES and so on. But I can't find some testing matrices and corresponding preconditioner to verify my program.
I know some ...
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Avoid arithmetic overflow in matrix multiplication
I am solving the following matrix equation for $\mathbf{x}$:
$$(J^{\mathbf{T}}J)\mathbf{x}=J^{\mathbf{T}}\mathbf{r}$$
$J$ is $m\times n$ matrix
$\mathbf{x}$ is vector of size $n$
$\mathbf{r}$ is ...
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Iterative methods to solve linear system in 3D FEM
I implemented a FEM solver in MATLAB for Poisson's equation in 3D, using hexahedron and sparse matrix for the Laplacian. I was using the backslash but now I have to use a few iterative methods (GMRES ...
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How to combine multigrid preconditioner with jacobi preconditioner?
I have not found any relevant information in the literature on the following rather simple problem:
How to combine (geometric) multigrid preconditioned conjugate gradient (MGPCG) with an additional ...
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210
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Library to solve dense linear system with GMRES
I have a fortran 90 code and I want to solve a dense linear system with GMRES. I would prefer the restarted GMRES with preconditioning. Is there some library that you know of that I could use? Now I ...
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PCJACOBI works but the default PCBJACOBI failed in PETSc
I am using PETSc and libmesh to solve a simple linear elastic problem with quite complicated geometry, using linear tetrahedral elements. I am always using the KSP CG as the solver.
I noticed that ...
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Flexible Conjugate Residual
If we want to use variable preconditioning in Conjugate Gradient, we can replace the Fletcher–Reeves by the Polak–Ribière formula (https://en.wikipedia.org/wiki/Conjugate_gradient_method#...
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how to implement ilu preconditioner for lsqr in python?
I am solving a least squares problem. Using lsqr is relatively slow. Is there a way to add a right preconditioner for lsqr?
https://docs.scipy.org/doc/scipy/reference/generated/scipy.sparse.linalg....
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Preconditioning the $[1 \quad-2 \quad 1]$ Finite Difference matrix
Let $A$ be the well known tridiagonal matrix coming from the 1D Finite difference discretization of the Laplacian, with stencil $\frac{[1 \quad-2 \quad 1]}{h^2}$.
The system $Ax = b$ is very large, so ...
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Automatic selection of the SLE solver and preconditioner during simulation
To simulate the physical process necessary to solve the arising systems of linear algebraic equations. The SLE matrix has a highly sparse form. There are a couple dozen non-zero elements in the string,...
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what is Sherman-Morrison formula
Can someone please explain what is the Sherman-Morrison formula and it's specialities when it comes to matrix calculations? I'm a little bit confused on understanding how the preconditioning works ...