# All Questions

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### Fast Algorithms for solving sparse LP problems

For solving a very sparse LP: {min $cx$: s.t.: $A_{m \times n}x=b$ , $x\geq 0$}, which one of the following algorithms is faster? Logarithmic barrier method Other variants of the interior point ...
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### Rational LP to integer LP

In the worst case complexity analysis of all the polynomial algorithms in linear programming such as ellipsoid method and interior point method, there is an assumption that the input data must be ...
3k views

### Eigenvalue decomposition of the sum: A (symmetric) + D (diagonal)

Suppose $A$ is a real symmetric matrix and its eigenvalue decomposition $V \Lambda V^T$ is given. It is easy to see what happens with the eigenvalues of the sum $A + cI$ where $c$ is a scalar constant ...
4k views

### When to stop Gauss-Seidel-iterations?

I want to have an estimation, that my solution has an error, let's say less than 1e-8. Usually, I stop the Gauss-Seidel algorithm, when the residual is "small enough" and this is already the problem. ...
1k views

### Is there an algorithm to find an almost-convex hull given a tolerance angle?

I'd like to know if there is an algorithm that given a set o points and an angle computes the convex-hull if the angle is $\alpha = 0$ and given an $\alpha > 0$ computes an envelope that follows ...
236 views

### How far is a non-symmetric discretization of an elliptic operator from the continuous operator itself?

I am investigating the accuracy and stability properties of a non-symmetric discretization of a Poisson problem. The problem originates from a ghost fluid discretization of the projection step of a ...
1k views

### Can post-processing use topoSet and createPatch without screwing up the results?

I would like to use patchAverage to obtain the average pressure on an object that consists of multiple patches (due to different boundary conditions), however ...
1k views

### Basin of attraction for Newton's method

Newton's method for solving nonlinear equations is known to converge quadratically when the starting guess is "sufficiently close" to the solution. What is "sufficiently close"? Is there literature ...
939 views

### Is busy waiting on both MPI_Iprobe and MPI_Testsome efficient?

I have an MPI application that needs to asynchronously respond to both incoming messages and request completions inside a dedicated communication thread. The obvious way to do this is a busy wait ...
1k views

### Explicit Euler method too slow for reaction-diffusion problem

I am solving Turing's reaction-diffusion system with following C++ code. It is too slow: for 128x128 pixel texture, acceptable number of iterations is 200 – which results in 2.5 seconds of delay. I ...
723 views

5k views

### BLAS/LAPACK subroutine to add two matrices with different offsets and leading dimensions

I currently searching for a subroutine from BLAS or LAPACK which realizes the following operation A = alpha*A + beta * B where A and B have different leading ...
2k views

### Software for 3D Navier-Stokes equation

What is the best software for solving and simulating the 3D Navier-Stokes equation for incompressible laminar non-Newtonian fluid flow?
115 views

### How to choose a stable PML for pseudo-spectral method with strongly varying velocity

My friend was working on this, and he asked me about the stability of PML while applying on pseudo-spectral method, I believe his concern was how to choose the difference(if the difference should be ...