691 questions
-2
votes
1
answer
61
views
Scientific calculator using js
I am buildinng a scientific calculator using js. The normal calculator part is working but my scientific calculator is not working. Earlier I was using `eval( function for calculation but due to ...
1
vote
1
answer
37
views
Compiled JAX functions slowing down for no reason
I am using Jax for scientific computing, specifically, calculating a pairwise interaction force across all the particles in my system in parallel. This is for a simulation of the dynamics of a ...
0
votes
2
answers
73
views
Finding maximum of multiple arrays in respect to their index, that can vary
Problem description:
I have got values that do correspond to specific conrer_ids, elements. From multiple sets of these values I need to find maximum ones and generate arrays containing conrer_ids, ...
1
vote
1
answer
417
views
Pivoted QR in Julia?
In Julia, the function qr(A) will perform a QR decomposition on a given matrix A. However, is there any function/way in Julia to do a "pivoted" QR decomposition on a given matrix?
- 805
0
votes
1
answer
181
views
How to initialize a container struct without knowing its size?
I am an amateur in C++, I am working on an scientific computing code. I defined a struct to store all the data input from the file. In the struct I have several 2D and 1D arrays whose dimensions ...
- 55
2
votes
0
answers
100
views
Diagonal Matrix of Sigma Values in Julia
If I compute the SVD of a matrix A in Julia, it will give the sigma values of the matrix, BUT NOT in matrix form. However, if I want to assemble the sigma values of a matrix A into a diagonal matrix, ...
- 805
0
votes
1
answer
888
views
Efficient/parallel matrix routines on Apple silicon
I'm working in Physics, and as part of my job I have to do a lot of numerical calculations ("numerics"), 90+% of which involves the diagonalization of large matrices. At the moment, I use ...
- 13
0
votes
0
answers
36
views
UnboundLocalError: local variable 'rmeff' referenced before assignment
Hey I'm trying to compute the concentration of a tubular reactor with two reaction, I get this error thrown each time I run the code, I tried putting the variable in the function as global still ...
1
vote
1
answer
700
views
When to use xarray over numpy for medium rank multidimensional data?
I have some multidimensional data and was wondering if i should use xarray when speed is one, albeit not highest, of my concerns.
I have a 4D array so it's not so big as to preclude me from using ...
- 127
3
votes
0
answers
341
views
How to calculate the path of a particle subject to a vortex?
I'm trying to draw a path of a particle starting at (x0,y0) subject to a vortex located at (xv,yv). This is inspired by Lorena Barba's AeroPython. As stated in the lesson, the motion should be ...
- 341
0
votes
0
answers
138
views
Is there an effective way to fit the following two datasets with lsqcurvefit?
I have two complex datasets for which I intend to find a suitable function to fit them. The first dataset is presented as follows:
As you can see, although complicated, it seems that this dataset is ...
- 3
0
votes
0
answers
76
views
pymc.Uniform giving ZeroProbability error: Stochastic alpha's value is outside its support, or it forbids its parents' current values
I am using a example given in web of pymc, when I try to run pymc.Uniform I am getting the following error
---------------------------------------------------------------------------
ZeroProbability ...
0
votes
1
answer
146
views
Finding the best linear section of data
I have some scientific data and wish to find the best region to fit a straight line in. Theoretically, the data should have a constant gradient but other influences effect the data such that there are ...
0
votes
1
answer
282
views
MATLAB: Does the execution of addpath/rmpath/savepath in one MATLAB instance affect other instances?
Does the execution of addpath/rmpath/savepath in one MATLAB instance affect other instances?
Motivation: Imagine that you are developing a MATLAB package, which provides a group of functions to the ...
- 266
0
votes
0
answers
272
views
Is MEX of MATLAB known to be slow on macOS?
Question: Is MEX of MATLAB known to be slow on macOS?
Here, "slow" refers to the speed of setting MEX up, of compiling MEX code, and of running the MEX function.
I have done some timing ...
- 266
2
votes
1
answer
429
views
How do I add another coordinate label in Xarray?
I have an Xarray, say
da = xr.DataArray([[1,2],[1,2]],coords={'x':['param1','param2'],'y':['idx','idx2']})
This is a 2D data array. As I build out my code, I would like to add another "column&...
- 127
1
vote
1
answer
307
views
SymPy `subs` Not Doing Anything
I have a differential equation for which I use sympy.solvers.ode.dsolve to solve, I get out
___________ ___________
-x⋅╲╱ E - V_max x⋅╲╱ E - V_max
ψ(x) = C₁...
- 55
2
votes
2
answers
776
views
Collect similar terms in sympy
I'm solving the Maxwell Garnett equation with SymPy:
solveset(Eq((e-m)/(e+2*m) = n*(a-m)/(a+2*m)), m)
Is it possible to simplify the solution by grouping similar terms together like Mathematica does?
...
- 33.8k
1
vote
1
answer
3k
views
Python equivalent for Matlab's fmincon for constrained nonlinear optimization
I'm currently trying to implement a Python script for solving a constrained nonlinear optimization problem with ~1000 variables and ~700 constraints (both linear and nonlinear). There already exists a ...
3
votes
1
answer
578
views
How to understand this number with "double scientific"-notation (~1e-9-4.999e-1) in matplotlib
I'm running a calculation that outputs a matplotlib plot with a vertical axis scaled with (see image below).
~1e-9-4.998e-1
This is very weird scaling and I'd like to make sure I understand the ...
- 1,182
2
votes
1
answer
1k
views
How to deal with large integers in NumPy?
I'm doing a data analysis project where I'm working with really large numbers. I originally did everything in pure python but I'm now trying to do it with numpy and pandas. However it seems like I've ...
- 1,155
-1
votes
1
answer
812
views
Writing Python Script to Solve System of Four Equations in Python w/ Four Unknowns [closed]
I have a system of four equations with four unknowns posted below. Each equation (f1,f2,f3,f4) is set equal to zero, and I have tried using fsolve with no success. The issue may be that these are non-...
- 19
1
vote
1
answer
308
views
Obtaining orthogonal left and right eigenvectors at similar computational speed in R/Python?
My goal is to find right and left eigenvectors of a diagonalizable, non-symmetric matrix m without inversion but so that they are still orthogonal to each other/ From ?eigen I would like to find the V^...
- 473
1
vote
1
answer
488
views
Python: is there a faster alternative to using numpy's polyfromroots?
Using Python, I am looping over a large collection of sets of roots (represented as a 2-dimensional numpy array, essentially), and forming each time the monic polynomial having the set of roots (...
- 113
1
vote
1
answer
595
views
Numpy (or scipy) binning of time series values based on timestamps
I'm trying to bin (downsample) a time series based on its timestamps. For instance:
import numpy as np
import pandas as pd
timestamps = np.linspace(0, 1000, 10000)
values = np.random.random(10000)
I ...
- 73
0
votes
1
answer
128
views
How to compare amplitude from Android with iOS
So I've read various posts and blogs on how to get the amplitude from the microphone on Android. Multiple posts suggested using this implementation:
minSize = AudioRecord.getMinBufferSize(
...
- 139
0
votes
1
answer
487
views
Fast fourier transformation in python using scipy
I am using scipy.fft module for calculating Fourier transformation of an array. Now using the module I got the transformation. But my question is how do I know the elements in the transformed array ...
1
vote
1
answer
480
views
cvxpy + mosek: The lower bound specified is not a number (nan)
In below code snippet I am trying to do a very simple linear regression using cvxpy and mosek solver
weight = df2['weight'].to_numpy()
A = df2[ regressors ].to_numpy()
x = cp.Variable(len(regressors ))...
- 221
2
votes
0
answers
364
views
How to implement shooting method with coupled ODEs
I want to simulate the laser power along a silica fiber. The ODEs and the used parameters can be found in the paper linked below. Note that I converted all units to SI units in my code. The authors of ...
- 21
2
votes
0
answers
70
views
Equivalent of `log1p` for matrices, aka `logdet_eyep`
Most scientific libraries (e.g. numpy/scipy) provide a numerically stable implementation of log1p(x) = log(1 + x) which yields sensible values, even when x is so small in magnitude that floating point ...
- 9,827
1
vote
0
answers
51
views
Ignore failed factorisations in numpy/scipy cholesky factorisations
I'm trying to compute the Cholesky decomposition of a large number of hermitian matrices,
import numpy as np
from numpy import linalg
H = np.random.rand(1000000,10,10)
H = 0.5*(H + H.transpose(0,2,1)) ...
- 335
0
votes
1
answer
598
views
Does sympy have an in built method to set multiple polynomials equal to each other?
Here’s a simple example of how i begin to attempt to solve a system of 2 equations in sympy. My goal is to first set equal to each other my equations:
import sympy as sp
x,y,z = sp.symbols("X, Y, ...
- 327
0
votes
1
answer
213
views
Filtering a noisy 1D time-series
I have a noisy, 1-Dimensional time-series, which I'd like to filter so as to obtain the contained "signal". The time-series in question is a collection of timestamps, each of which ...
- 465
1
vote
1
answer
202
views
Need an efficient way to plot planes from large sets of 3D coordinates
I have some detector data collected on a 2D camera, I then convert it to a lab frame so I end up with an (x^2+y^2) and z coordinate for each pixel in the image. But then the object rotates about it's ...
- 13
2
votes
1
answer
1k
views
Optimize performance on a SLURM cluster
I am writing you after many attempts I have done on a CPU cluster so structured:
144 standard compute nodes
2× AMD EPYC 7742, 2× 64 cores, 2.25 GHz
256 (16× 16) GB DDR4, 3200 MHz
InfiniBand HDR100 (...
- 23
1
vote
0
answers
278
views
How do I solve this differential equation using sympy or py-pde?
I would like to solve the following inhomogeneous partial differential equation:
I have been reading the documentation for py-pde and figure I should make a 'ScalarField' object representing the RHS, ...
- 69
2
votes
0
answers
118
views
MatrixFree Linear Operators vs. Sparse Arrays
How to quantify the performance of matrix-free operators and sparse arrays for matrix-vector products. Specifically, what is speed cost of having matrix-vector products dominated by function calls ...
0
votes
2
answers
629
views
Using Sympy: TypeError: '>=' not supported between instances of 'NoneType' and 'int'
So, I have this code below:
from sympy import Symbol, solve, nsolve
x1 = Symbol('x1')
x2 = Symbol('x2')
w1 = Symbol('w1')
w2 = Symbol('w2')
eq1 = w1 + w2
eq2 = (w1 * x1) + (w2 * x2)
eq3 = (w1 * x1**...
- 139
4
votes
1
answer
278
views
How to speed up this for loop containing kronecker product?
I want to speed up the following for loop.
% Use random matrices for testing.
% Elapsed time of the following code is around 19 seconds.
% So, when N is large, it's very slow.
n= 800; N =100; k =10;...
- 151
3
votes
2
answers
56
views
Obtaining columns of a matrix satisfying multiple booleans in Julia
I am trying to obtain only those columns of a matrix that satisfy two or more boolean conditions. More specifically, I am trying to find only those eigenvectors of a matrix based on certain ...
- 119
0
votes
1
answer
784
views
Scatter plot for points in an array above a given value
import matplotlib.pyplot as plt
import numpy as np
fig = plt.figure()
eps = 0.8
X = np.linspace(-1, 1, 100)
Y = np.linspace(-1, 1, 100)
X, Y = np.meshgrid(X, Y)
Z = np.exp(-X**2-Y**2)
data_zero_x =...
- 85
1
vote
3
answers
198
views
How to split a user inputted list of 8 numbers into quarters
Currently, I have
data = input('Please input 8 numbers \n')
What I want to do is split this list into quarters so I may input them into matrices A and B of a 2x2 format
- 11
0
votes
1
answer
31
views
Trim for loop between datapoints from a 2d array
I loaded a file.dat as a 2d array
data = np.loadtxt('file.dat')
I have used a for loop as to iterative over all points in this array
for i in range(len(data):
If I wanted to only do a for loop ...
- 13
0
votes
0
answers
157
views
Numpy/Python Scalability
I use Python and Numpy mainly for scientific programming. A typical task is to construct and then diagonalize many medium-sized matrices. I try to avoid any for loops and mainly use advanced numpy ...
- 359
1
vote
0
answers
261
views
Eclipse IDE for Scientific Computing for C++ on windows
I have installed the latest version of Eclipse IDE for scientific computing 2020-12. I am trying to run an MPI c++ project but I get this error :
Program "mpic++" not found in PATH
I have ...
- 580
0
votes
1
answer
562
views
Why VisualBasic (VB.NET) faster than C++ code in this example?
I have been benchmarking an iterative calculation, a Lapalace equation solver for electrostatics, that uses the Jacobi method. I wrote the same algorithm in Visual Basic and C++ (and other languages ...
- 36
2
votes
1
answer
96
views
Collapse Numpy arrays to scalar when, e.g., multiplying by zero
I'm a bit surprised that I couldn't find an easy when to collapse dimensions of a Numpy array containing identical values. Let me explain.
I might have to multiply to time series implemented as arrays,...
- 967
0
votes
1
answer
61
views
Is there a good framework or package in python to compare something over a number of parameters?
When working in python for research I often end up with some problem where I want to compare a result over a different number of parameters.
params1 = [0.1, 0.2, 0.3]
params2 = [5, 10, 50]
parmas3 = ...
- 1,411
1
vote
0
answers
221
views
`map_blocks` leads to tuple indices error in Dask
I am trying to apply a simple operation in parallel on a datacube, but I keep running into
a TypeError.
This is my input datacube (called dcube):
<xarray.DataArray 'A' (time: 6, pol: 1, y: 823, x: ...
- 3,098
0
votes
1
answer
712
views
Create uniformly spaced points in a given direction
Suppose I have a line in 2D and in an arbitrary direction. I would like to create uniformly spaced points along this line. I thought of one way to code this but seems like it can get messy, are there ...
- 63