# All Questions

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### surface: rows (Z) must be the same as length (Y) and columns (Z) must be the same as length (X) in octave

I am having a dataset and trying to plot a 3-d plot between the independent and dependent variables.but, I am getting this error whenever I am trying to plot here is my code: ...
2answers
39 views

### Dyadic operations, fourth order tensors and Tensor algebra

I am trying to understand the dyadic operation for a while since I am interested in Elasticity problems. I believe an intuitive understanding (rather than assuming) will give me good problem solving ...
0answers
9 views

### Fitting using curve_fit of scipy in python gives totally different answer for 1/t and t

I was trying to fit some data to a single degree exponential decay function but a*exp(-x*t) and a*exp(-x/t) gives completely ...
1answer
60 views

1answer
98 views

### How do I calculate the Jacobian of this function?

I have two vectors $r$ and $m$. Both vectors are $N\times1$. A function is calculated as - $F(1:N) = \phi r + (r^3 + rm^2)$ $F(N+1:2N) = \phi m + (m^3+mr^2)$ ...
0answers
51 views

### Problems with 'ODEint - Excessive work done' and using pySINDy

I am create syntetic data from a system of differential equations describing the COVID-19 epidemic and then I try to use the method SINDy to recreate the differential equations from the data. Link to ...
1answer
80 views

### discretizing surface integral using nodal DG method

I am currently learning nodal DG methods, primarily through the book by Warburton, and am a bit confused on how to handle surface integrals using straight edged elements. On page 187 (and on page 214)...
0answers
37 views

### 2d Ising model simulation (Python) [closed]

There were some problems occurring while I was simulating 2d Ising model. In short, I cannot get the correct "energy-temperature" relationship. Please tell me what's the problem in my ...
1answer
55 views

### GNU Octave: using 'parallel' with an array (apply function to each array member)

I am new to GNU Octave 6.2.0 on Linux, and I am trying to use the package 'parallel' to make use of 24 threads on my machine. I have an array (array1) that has ...
1answer
169 views

### Translating the Euler code in scipy's solve_ivp

My code is based on the similarity transformation X=VZ.I simulate the model for transformed equations involving Z by replacing ...
3answers
22k views

### BFGS vs. Conjugate Gradient Method

What considerations should I be making when choosing between BFGS and conjugate gradient for optimization? The function I am trying to fit with these variables are exponential functions; however, the ...
0answers
41 views

### Constrained optimization for non-linear equations in octaveGNU

I have installed Optim1.6.1 package. I would like to solve a system of equations in non linear finite element analysis using constraints as u=1 at certain nodes. u=0 at certain nodes. Typically I find ...
1answer
113 views

### Interpreting multivariable root-finding results from Matlab's fsolve algorithm

Edit: So I was able to get the same value of r that's given, when coding up the sum of squares of function values directly in the script file, rather than on the Command Window. So, maybe there's a ...
0answers
20 views

### Optimization A* Path finding for C# [closed]

I am creating a game in Unity and have implemented an A* algorithm to do my pathfinding. For 1-3 squares away it performs just fine. But more than that it starts slowing the program down and at 10+ it ...
0answers
88 views

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1answer
76 views

### How is a wall boundary implemented (using ghost cells) in a simple 2d euler flow solver?

I understand that you must reflect the velocity of the cell across the wall and store that reflected velocity in the ghost cell (which will then be used for flux/residual calculations), but that is ...
1answer
115 views

### How to extract connected components from persistence diagram?

From the given point cloud (Fig. 1), I use Scipy-TDA to extract persistence diagram (Fig. 2). What I'm interested in is to extract 3 circles. For example, I'd like to know 3 center points and labels ...
1answer
382 views

### 4th order tensor rotation - sources to refer

I am trying to model a linear elastic material in Abaqus using a UMAT. For my application, I need to rotate the 6x6 compliance matrix for a given set of eigenvectors (or a rotation matrix). I came ...
1answer
170 views

### Pseudospectrum of non square Matrix in Python

I have a rectangular matrix $A \in \mathbb{R}^{m \times n}$ ...
0answers
33 views

### How to derive amplification factor for RK4(Runge Kutta method of order 4) - CD2 scheme for one degree hyperbolic function? [closed]

I tried deriving the expression but the different slopes in the RK4 method are confusing. Moreover, when I am referring to various sources I get the same expression for amplification for any spatial ...
2answers
65 views

### Reference for mass matrix assembly

I will now explain what I understand to be the process of a finite element mass matrix assembly. I would like a reference which does something similar, or if I am mistaken about the process please let ...
0answers
13 views

### Can Catboost Regressor be leveraged for ordinal regression?

Customer satisfaction is generally an ordinal variable on a scale of 1 - 5, where 5 is the best score. Ordinal regression is used to regress such variables. Can Catboost Regressor, handle such a ...
1answer
58 views

### Improving efficiency of FFT for large time window and single frequency pulses

Spectral methods for pulse propagation usually require at least one FFT and one iFFT for each step. In my case I have a two-dimensional radially symmetric electric field (one dimension in space, one ...
1answer
85 views

### Calculating the Jacobian for a function containing a derivative

I have the equation $F(t) = \phi u + \frac{1}{2}\frac{d^2u}{dt^2} + u^3$ and broadly speaking, my task is to calculate the $\phi$ and $u(t)$ such that $F(t) = 0$. I am testing out a new algorithm to ...
0answers
36 views

### Gmsh and an exactly symmetric model [closed]

I have a 2D region that is symmetric with respect to an axis and needs to be studied in isolation. It's an elasticity problem and I hope to get eigenvectors as much as possible symmetric or anti-...
2answers
48 views

### Passing in user inputs with mpirun

I am building a quantum circuit simulator using mpi4py. The simulator takes user inputs to build the initial system and quantum gates the system passes through. I can get the code to work if I do not ...

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