# All Questions

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62 views

### Quick scheme for separable first-order ODE

I'm trying to integrate an incredibly simple ODE: $$y'(x) = -f(y),\quad y(0) = y_0 \ ,$$ from $x=0$ to $x=1$. This is a decay type of equation, $f$ is the (variable) decay rate and $y$ is the ...
620 views

### Efficient Implementation of the Log Sum Exp Log trick for Preventing Underflow erros

So I'm constructing a Gibbs sampler for a moderately sized graphical model, and I started encountering underflow errors (the computed relative frequencies were all very small). To get around this, I'...
249 views

### Calculation of phonon dispersion

I have a couple of conceptual questions regarding the calculation of phonon dispersions. I wish to calculate the phonon dispersion of Nickel with my lattice vectors given by , [1-10] and [11-2] (...
77 views

### Solving condensate density problem in MATLAB

I want to solve for $n_{0}$ for a fixed value of $n$, lets say $n=1$ $$n= n_{0}+ \dfrac{1}{2}\int_{-1/2}^{1/2}dq\left(\dfrac{e_{q}+Un_{0}}{\hbar\omega}-1\right)$$ where $e_{q}=2[1-cos(2\pi q)]$ ...
65 views

### approximation of nonlinear time-dependent system with history

I have two time-dependent coupled equations. One of which is several orders of magnitude more computationally demanding than the other. I am trying to use machine learning to reproduce the behavior of ...
397 views

### how to pick a submatrix of a sparse matrix quickly(matlab)

I have a large sparse matrix A and i want to pick the submatrix of it to do block jacobi iterations. For the blocks, i have get a matrix Q that contains the index of nonzero entries in its Jth column ...
165 views

55 views

### Simulating magnetic particles in a field free point generated by two opposing magnets

This is probably a long shot with such a short time, but I've been trying to get theoretical data for a project I'm working on. The project involves using a very simplified version of magnetic ...
70 views

### Finite element convergence rate and possion's ratio

I am running simulations of a cantilever beam where it is fixed on one end and negative force applied to the other end. The first simulation is with 4-node linear quadrilateral elements and the other ...
23 views

### Semi-Definite relaxation of non-linear constraint?

I am implementing an optimization problem using semi-definite approach. One of my constraints is of following form $trace(A∗X)−(k∗trace(A∗X))+(k∗\sqrt {(trace(B∗X)} )==0$ where k is a constant, A ...
235 views

### Gauss-Seidel method convergence

I am currently programming a code to find the equilibrium function that satisfies the poisson equation in 2D. In order to do this I use finite difference methods and the discrete equation I want to ...
605 views

### Eulerian vs Lagrangian vs Mesh-based vs Meshfree/Meshless methods

Hailing from the scicomp community recently getting into computer-graphics, I have noticed that the scicomp communities talk about mesh-based methods like FDM, FVM, FEM, etc, vs meshfree or meshless ...
141 views

810 views

### Any note on Immersed boundary finite difference method?

For parts of a talk, I need a note on "Immersed boundary finite difference method", mainly about the reason of appearing this branch in the finite difference methods, considering mathematical ...
14 views

### Implementing Housholder QR decomposition in Python

I am struggling to get my implementation of householder qr decompostion to generate the correct answers. I have been working on this for days and cannot workout where my code is going wrong. Any help ...
32 views

### Are 2nd spatial derivatives useful for integrating ODEs?

In discussion of adaptive integrators for ODEs, I see a lot of discussion of how second derivatives in time can be approximated using finite differences, i.e., take several steps, and use numerical ...
63 views

### 2D Heat equation - MatLab implementation (FD in space, Expl. Euler in time)

I'm trying to solve the heat equation in 2D in $\Omega=[0,1] \times [0,1]$, with homogeneous Dirichlet boundary conditions, and initial condition $u(x,y,0)=\sin(2 \pi x y)$ i.e. \begin{cases} u_t=u_{...
15 views

### How to use the norminv function in excel

I am given a list of ages from 29-73 and I am asked to calculate what values fall within the middle $95%$,top $10%$, and $P20$ Any help would be greatly appreciated
50 views

### Calculate accuracy order/rate

I was doing error analysis of numerical scheme and I get $L_1$ error for each grid size with $N$ element. I was searching reference to compute accuracy order/rate from that error data but doesn't find ...