# All Questions

7,679 questions
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### The final Boundary Condition is Unknown, Is Backward Euler is still valid to be implemented?

I am working on conductive polymer modeling and supposed to do one-dimensional diffusion model in the thickness of the polymer, however, due to the small value of thickness in micro, when I use the ...
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### Fastest method for elliptic pde

What is the fastest method (language, solver, etc.) to numerically solve elliptic equations such as Poisson or Stokes equations in a cube in 3D with mixed boundary conditions? Especially, a ...
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### Inverse kinematics BFGS divergence

I am trying to implement inverse kinematics solver using BFGS as stated in the paper Xia2017. In the test experiment, i created 4 objects in 3-dimensional space: Node,Node1,Node2,Node3. Each Node is a ...
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### Why does the correlation function of this stochastic differential equation starts at different points?

I am working with the following differential equation: The equation is $$x=\beta +\sqrt{2D} \xi(t)$$ where $\xi(t)$ is a white noise term, with a reflecting wall boundary conditions. After solving ...
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### How to implement adaptive step size Runge-Kutta Cash-Karp?

Trying to implement an adaptive step size Runge-Kutta Cash-Karp but failing with this error: ...
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### Finding a shortest path in a graph

If each edge of a graph $G$ is unweighted or has equal weights, then the shortest path between two nodes in that graph is the path that contains the fewest number of edges. Such a path can be obtained ...
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### Infinity norm inverse estimate

Let $V_h$ be the space of linear finite elements on triangles. From the scaling argument, we can obtain the following inverse estimate inequality: $$\| v_h \|_t \leq ch^{m-t} \| v_h \|_m,$$ for ...
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### Calculate the Bloch wave

The eigenvalue problem $$\frac{d^2u}{dx^2}+2i k\frac{du}{dx}-k^2-6\sin(x)^2u(x)=-\mu u(x)$$ gives the first five eigenvalues with $k=0$ or $k=1$ which are $2.06$, $2.26$, $5.16$, $6.81$, and $7.74$....
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### How to improve the efficiency of periodicity detection for long time based lined and gapped datasets

Our data set has $10^4$ data points, but has a long baseline and many gaps. As the histogram shows, the horizontal-axis is time and most of the time, there are no data. The vertical-axis is data ...
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### Numpy repeat for selected rows [closed]

Is it possible to repeat selected rows in numpy? For example, can we get [[1, 2,3][1,2,3][4,5,6]] from[[1, 2,3][4,5,6]] ?
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### extrapolation/interpolation in fmincg.m

Can you tell me these equations come from where in MATLAB fmincg.m? ...
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### Is a symmetric bilinear form necessary to ensure a weak formulation has a solution?

Problem I want to convert the general second order linear PDE problem \begin{align} \begin{cases} a(x,y)\frac{\partial^2 u}{\partial x^2}+b(x,y) \frac{\partial^2 u}{\partial y^2} +c(x,y)\frac{\...
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### How to decrease the cost by direct computation of the jacobian given a system of equation with drift matrix

I have provided the R script of the project I´m working on.It works fine but computation of the required Jacobian at each step makes it costly. I need to find an alternate way to either compute the ...
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### Properly sizing ParaView plots for LaTeX

I would like to make a visualization with ParaView for a paper. In order to have a high quality look, I would like the image to be, say, 300 dpi (or vector graphics). Moreover, since I know the column ...
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### A fast way to check if a Matrix is ill-conditioned, and turning it into well-conditioned

I'm running a simulation, and some linear solvers are returning a message of ill-conditioned matrix. Hence, I'm looking for a fast, easy to implement, method to detect if a matrix is ill-conditioned, ...
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### Polyfit min/max constraints

I would like to "smooth" my prediction output and limit it to specific local min/max points. (The predicted line in blue - min is to low, how can I limit the polynomial equation accordingly?) My ...