# Computational Science Stack Exchange Community Digest

## Top new questions this week:

I am considering the problem of simulating the evolution of an interface given as a curve in 2D (or surface in 3D) that evolves according to a velocity specified at the interface of the form: $$\vec{v}... pde matlab numerics differential-equations advection  asked by B0bby31 Score of 3  answered by ConvexHull Score of 4 ### A question related with p-Laplacian and conjugate gradient method I have the following energy functional of p-Laplacian equation:$$ E(u) = \frac{1}{p} \int_{\Omega} |\nabla u|^p dx $$for 2.8 \leq p \leq 5. My goal is to minimize the energy functional by using ... finite-difference convex-optimization nonlinear-programming conjugate-gradient  asked by User124356 Score of 3  answered by whpowell96 Score of 2 ### Discontinuous Galerkin for transport equation with non-constant advection This question is mainly an inquiry about the usefulness of Discontinuous Galerkin (DG) for the time-independent transport equation of the form$$\sigma u+\beta\cdot\nabla u =f,\;\;\;\text{on }\Omega\...

 asked by UserA Score of 2

### The error propagation in calculating the inverse using a matrix decomposition

I have been trying to calculate the matrix inverse of some large matrix with entries ranging by orders of magnitude. I tried to use the matrix decomposition to simplify the computation, where a matrix ...

linear-algebra error-estimation matrix-factorization inverse
 asked by ShoutOutAndCalculate Score of 2

### Is the Hessian of the strain energy of a hyperelastic material positive definite in general

Is the spatial second derivative of the strain energy of a hyperelastic material positive definite in general? If this is not a general property of hyperelastic materials are there techniques for ...

optimization matrix-factorization nonlinear hyperelastic
 asked by Olumide Score of 2

Crossposted at MathOverflow Consider a quadratic programming problem with the following format: $$\text{min} Q(x) = c^Tx+\frac{1}{2}x^TDx \\$$ $$\text{s.t.} Ax\leq b, \\ x\geq 0$$ where $D$ is a $... linear-algebra optimization constrained-optimization convex-optimization nonlinear-programming  asked by ximeng fan Score of 2 ## Greatest hits from previous weeks: ### How do I calculate the numerical difference between two fields stored in two different VTK files with the same structure? Suppose I have two VTK files, both in structured grid format. The structured grids are the same (they have the same list of points, in the same order), and there is a field, call it "Phi", in each VTK ... visualization vtk  asked by Geoff Oxberry Score of 16  answered by Geoff Oxberry Score of 16 ### In FEM, why is the stiffness matrix positive definite? In FEM classes, it's usually taken for granted that the stiffness matrix is positive definite, but I just can't understand why. Could anyone give some explanation? For instance, we can consider the ... finite-element matrix stiffness  asked by user123 Score of 14 ### How can I determine the period of my pseudo-random number generator? Suppose I'm using a linear congruential pseudo-random number generator (PRNG). Given a seed$x_0$, the multiplying factor (a), the shift factor (c) and the modulus factor (m), how can I determine the ... random-number-generation  asked by Paul Score of 16 ### Gradient descent and conjugate gradient descent For a project, I have to implement these two methods and compare how they perform on different functions. It looks like the conjugate gradient method is meant to solve systems of linear equations of ... optimization conjugate-gradient  asked by Philipp Score of 12  answered by Elaine Hale Score of 18 ### Constraints involving$\maxin a linear program? Suppose \begin{align*} \min A &\mathrm{vec}(U) \\ &\text{subject to } U_{i,j} \leq \max\{U_{i,k}, U_{k,j}\}, \quad i,j,k = 1, \ldots, n \end{align*} whereU$is a symmetric$n\times ...

optimization linear-programming
 asked by N21 Score of 16
 answered by Geoff Oxberry Score of 14

### Tikhonov regularization in the non-negative least square - NNLS (python:scipy)

I am working on a project that I need to add a regularization into the NNLS algorithm. Is there a way to add the Tikhonov regularization into the NNLS implementation of scipy [1]? [2] talks about it, ...

optimization convex-optimization nonlinear-programming regression scipy
 asked by user3259573 Score of 4
 answered by Brian Borchers Score of 20

### Python vs FORTRAN

Which one is better: FORTRAN or Python? And I guess that in both cases you need Gnuplot, am I right? I'm working on a Windows machine at the moment. I'd like to use it to get numerical solutions for ...

python fortran
 asked by Nick Score of 20
 answered by Geoff Oxberry Score of 36
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