Questions tagged [numpy]
NumPy is the fundamental package for scientific computing with Python.
27
questions with no upvoted or accepted answers
8
votes
0answers
586 views
Fast Automatic Differentiation for numpy?
I would like to use automatic differentiation to calculate gradients to function written in numpy.
I've come across a number of packages, including
autograd
tangent
chainer
But none of them seem ...
7
votes
0answers
166 views
fastest way to compute many small dot products
I have two n-by-3 blocks contiguous in memory ("n vectors of length 3") and I'd like to compute the dot product between each of the rows as fast as possible. In numpy, using ...
5
votes
0answers
1k views
Python - calculation time derivative and laplacien by finite differences
I would like to determine a temporal derivative and a Laplacian by the finite differences method to solve the heat equation in a 1-dimensional case. My aim is to get the sources term that is why I ...
3
votes
0answers
90 views
Inconsistency in optimize.minimize
I am trying to fit a time-dependent curve at each time step. I do so in minimizing along $x_c$ the quadratic error between the curve and a reference solution $ 1/(1 + \exp\left(\sqrt{S}(x-x_c)\right) $...
3
votes
0answers
2k views
Efficiently creating an adjacency matrix from a lattice in numpy
I have an $n$ by $m$ numpy array representing a rectangular lattice $L$, where each site contains a one or a zero, representing two different materials. I'm modelling heat flow across this lattice. ...
3
votes
0answers
246 views
matplotlib contourplot for $\log z$ in the Complex Plane $\mathbb{C}$
I tried using Python's matplotlib on the logarithm and here is what I got, a kind of starburst pattern. Since the angle jumps between $\theta = 0$ and $\theta = 2\pi$, contour assumes there is a ...
2
votes
0answers
189 views
Optimizing for loops by using Einstein summations instead
I have some Python code containing a couple of for loops, which I would like to optimize by using low-level functions. My first approach is to use ...
2
votes
0answers
97 views
Is the numerical resolution of this huge sparse polynomial system tractable?
I'd like to find numerically a solution to a sparse system of 2000000 polynomial equations of degree 3 with 50000 variables and integer coefficients (or at least to decide whether or not a solution ...
1
vote
0answers
30 views
Interpolate location based on triangular sensor array
There are 3 sensors (A, B, C) on a plane, located in the corners of a (known) equilateral triangle.
I want to calculate the (2D) location of an object (X) inside that triangle.
One sensor returns one ...
1
vote
0answers
58 views
Help with vectorized computation where vector multiplication would need to create an additional dimension
I want to use vectorized computation (with python and numpy) to do some calculation involving bessel functions.
As is often the case, I need to calculate the sums of bessel functions of (infinit) ...
1
vote
0answers
18 views
Problem with recursive implementation of Subspace Iteration method in Numpy
I am having trouble with implementing the method of subspace iteration to find the eigenvalues and vectors of a random, symmetric matrix, A that is mxm with m = 10. ...
1
vote
1answer
82 views
How do I find the portion of a cell/voxel lying within a defined surface?
We have a 3-dimensional grid of voxels (or cells), with individual voxels being of volume $dx\,dy\,dz$ where $dx=dy=dz=1$.
A cone-like surface is defined by some function, $z = f(x, y)$, which in ...
1
vote
0answers
77 views
Calculate integrals using numpy.fft
Good evening,
I would like to understand why I do not get the correct result:
I assume that I know my function on discrete data points and expand it as a discrete Fourier transform: $\text{sin}(x)=\...
1
vote
0answers
109 views
computing dual matrix trace norm and tensor gradient in python
I'm trying to write the following function in python:
$$
f_\mu(\mathcal X) = f_0(\mathcal X) + \sum_{i = 1}^n \max_{||\mathcal Y_{i(i)}|| \leq1} \alpha_i\langle \mathcal X_{(i)},\mathcal Y_{i(i)} \...
1
vote
0answers
234 views
Rank filter on an nXm array using python
I would like to apply a rank filter on an nXm numpy array. Let's say I have this array:
...
1
vote
0answers
49 views
Update model parameter with new data, discarding old data
I have this dataset, and I am using y = (a * x^n) / (b + x^n) Hill function as the model, where a is the limit of the Hill curve,...
1
vote
0answers
1k views
Finding eigenvectors and eigenvalues of large matrices in Python's numpy
I am running a PCA analysis on a data set using Python's (v2.7.10) NumPy. I validated that my program works by running the PCA analysis on a smaller dataset and then confirming that I get similar ...
1
vote
0answers
208 views
Inverse quadratic method only makes one iteration - python
I'm tryin' to implement this method with python3 but i don't solve the problem. This is my code:
...
1
vote
0answers
943 views
PageRank computation as the left principal eigenvector
I'm following the book here to compute PageRank: http://nlp.stanford.edu/IR-book/html/htmledition/markov-chains-1.html
I built the transition matrix P as indicated in the book. Then I computed the ...
0
votes
0answers
53 views
how can I plot specific iterations?
I have made this code for an explicit Euler method but I want to plot only the 0,1,25,50 iterations not all of them.How can I do it?
...
0
votes
0answers
137 views
How to take convolution of two arrays in Python by using NumPy?
Generally, we know that if we have this relation between Fourier transforms of three functions in frequency domain as:
$$\mathfrak{F}\{\mathsf{P}(t)\} = \mathfrak{F}\{\mathsf{Z}(t)\}\mathfrak{F}\{\...
0
votes
0answers
64 views
How to plot a function for multiple values of a parameter in the same set of axes in Python?
I'm currently trying to plot a graph wich describes a photoionization cross section as a function of incident photon energy for optical transition in a semiconductor for different values of the $\...
0
votes
0answers
94 views
Smoothing FFT result
I am trying to calculate the spectrum of Bremmstrahlung, which involves calculating the Fourier transformed acceleration. I am solving a non-linear ODE to numerically calculate the acceleration in the ...
0
votes
0answers
228 views
What algorithm do BLAS and ATLAS use for matrix multiplication?
I have searched and what I understood was that they use the naive one with several memory and cache optimizations.
However, I wanted to know whether they are using the Strassen or the Coppersmith-...
0
votes
1answer
68 views
Specifying mesh spacing for DFT in numpy
I was testing the .fft package of numpy 1.16.1 in Python 3.7.2. In particular I was trying to verify that the transform resembles the analytical one for: $$f(x) = \mathrm{exp}\left[-\left(\frac{x-5}{2}...
-1
votes
1answer
66 views
plotting $F=K \frac{q_1 q_2}{r^3}$ in python
I tryin to plot the position of electron in the hidrogen atom by Coulomb's law,
$F=K \frac{q_1 q_2}{r^3}$
This is mi code
...
-1
votes
1answer
85 views
Solve integral $ \int_{-\infty}^{\infty} e^{-x^2}dx$
i trying to solve this integral
$$\int_{-\infty}^{\infty} e^{-x^2}dx$$
I'm using this
CODE
...
