# Questions tagged [numpy]

NumPy is the fundamental package for scientific computing with the programming language Python.

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### Cython functions for generating NumPy date ranges

I have rewritten my python code in cython in order to speed up it quite a bit. However after checking the code in jupyter it seems that part of it is still compiled as python code, therefore its not ...
1answer
113 views

### Calculating difference statistics over a moving window

I'd like to calculate some statistics of given data (frequencies of difference among elements on various distances in percent multiplied by 10) using moving window within that data. Is it possible to ...
1answer
41 views

### Python - How to efficiently bin multiple dependent variables to a common independent variable?

Setup: I have ~30 parameters (dependent variables) measured simultaneously along a common time axis with ~1Hz resolution (independent variable). I need to calculate bin averages for all parameters, ...
1answer
46 views

### Trapezoidal rule for set of data

Here is the question from the book of Mark Newman-Computational Physics Exc 5.1 a) Read in the data and, using the trapezoidal rule, calculate from them the approximate distance traveled by the ...
1answer
100 views

### Implementing numerical integration in Python

I have this Python code that implements a rectangular numerical integration. It evaluates the (K-1)-dimensional integral for arbitrary integer $K \geq 1$ \int_{u_K = 0}^{\gamma}\int_{u_{K-1} = 0}^...
1answer
79 views

### Optimising iteration and substitution over large dataset

I have the following code: ...
3answers
8k views

### Gradient descent for linear regression using numpy/pandas

I currently follow along Andrew Ng's Machine Learning Course on Coursera and wanted to implement the gradient descent algorithm in python3 using ...
1answer
104 views

### Ensuring performance of sketching/streaming algorithm (countSketch)

I have implemented what is know as a countSketch in python (page 17: https://arxiv.org/pdf/1411.4357.pdf) but my implementation is currently lacking in performance. The algorithm is to compute the ...
2answers
81 views

### Find the next predicted time a satellite is going to take picture of place

create a function which predicts the next time a satellite image will be taken of a certain location. When there is enough data to do so, the function should print a prediction for when the next ...
1answer
40 views

### Schelling's model of Segregation Python implementation with Geopandas

If you don't know what is Schelling's model of segregation, you can read it here. The Schelling model of segregation is an agent-based model that illustrates how individual tendencies regarding ...
1answer
78 views

### Picking seats in a matrix

I'm trying to write a Python class that creates a matrix of zeros, then uses a random number generator to pick 'seats' on the matrix. It changes the zero in that seat to a one, until the matrix is all ...
1answer
304 views

### Efficiently selecting spatially distributed weighted points

Background: Motivation behind writing the following code is originated in the area of computer vision. More specifically – image rectification. In order to obtain rectified images, one has to find a ...
4answers
9k views

### Processing an image to extract green-screen mask

I am using OpenCV to process an image, and in my code, I have to check / edit each pixel separately: ...
2answers
49 views

### Read coordinates from many files and calculate polygon areas

My goal with this snippet is to create an array of coordinates which in turn is a tuple of 68 elements, area and modified area array for all 10k elements and assign it to the ...
1answer
138 views

### Bilinear image interpolation

I have written a bilinear interpolant, which is working moderately well except that is painfuly slow. How can rewrite the code to make it faster? Using opencv directly isn't a valid answer. ...
1answer
70 views

### Game of life using NumPy

I'm trying to improve my Game of life program for school in Python, to be able to run it quicker. So if you have some ideas, I will be glad to hear them. My current code: ...
1answer
2k views

### OpenCV 3: Using k-Nearest Neighbors to analyse RGB image

I'm new to computer vision and numpy. I wrote a simple script to seperate red, green and blue colors from the original image by using the kNN algorithm. After reading through some numpy tutorials, I'...
1answer
77 views

### Evaluate joint probability density function of a Markov random field

The following code evaluates probability mass function for all possible states of a model. ...
2answers
60 views

### Grouping sorted coordinates based on proximity to each other

I created an algotrithm that groups a sorted list of coordinates into buckets based on their proximity (30) to one another. Steps: Create a new key with a list ...
1answer
56 views

### Hurst Exponent calculator

I am aiming to compute the Hurst Exponent of a 1-D signal time series in Python. For now, I have one existing function hurst(sig) which returns the Hurst exponent ...
3answers
515 views

### Generating Julia set

So, I just wanted to post something on Rosetta Code, and I found this task of generating and plotting a Julia set: http://www.rosettacode.org/wiki/Julia_set. There was already one solution but it was ...
1answer
33 views

### Converting string of hex values to numpy array of specific shape

I am working on a project that needs to take a .bdf font file and turn it into a Numpy array. I am using the code below to turn the bitmap for the font into a numpy array. It currently works, I just ...
1answer
50 views

### Select optimal piecewise regression fit

I'm making a program which fits a piecewise linear regression with up to 4-5 breakpoints in the data, and then deciding how many breakpoints is best to prevent over and underfitting. However, my code ...
2answers
94 views

### Calculate mean and standard error of a generator in Python

The goal of the following code is to calculate the mean and the standard error of vectors of randomly-generated numbers. I am looking for feedback both on the correctness of the calculation, and on ...
2answers
390 views

### MNIST Deep Neural Network in TensorFlow

I have been working on this code for a while and it gave me a lot of headaches before I got it to work. It basically tries to use the MNIST dataset to classify handwritten digits. I am not using the ...
2answers
27k views

### Crop black border of image using NumPy

Objective: Crop the image so only the number stays in the image Problem: Slow Performance I have code that crops an image. The image pixels are 0 or 255. There are no values between. The ...
2answers
111 views

### Performance issues with double for loops, EM-algorithm

The alpha that I create is not created in a crazily efficient way I know, but the main bottleneck in this code is in what I call the "Maximization step" (see comments in code). There are double for-...
0answers
28 views

### Parsing and plotting with numpy (or pandas)

I am trying to improve the following code to make it more broadly applicable and quick to use. ...
1answer
51 views

### Nested list performance tuning

I need to make a function like these two, but at least an order of magnitude faster in python. Any tips or tricks? These functions inputs are nested lists, like: ...
3answers
890 views

### KenKen solver - Python

Here is my code for the KenKen puzzle: The user must fill in each embolded regions with numbers in the range 1-n where n is the board dimensions (e.g: 4*4, n=4) ...
1answer
66 views

### Generating Latin hypercube samples with numpy

I wrote some code to generate Latin hypercube samples for interpolation over high-dimensional parameter spaces. Latin hypercubes are essentially collections of points on a hypercube that are placed on ...
1answer
807 views

### Plotting polynomials roots

NOTE: See follow up to this question here I created a simple python script to plot quadratic, cubic and quartic polynomials with integer coefficients between -4 and 4. It uses numpy to find the roots ...
1answer
88 views

### Agent based model in Python

My model is based on the Ultimatum Game. I won't go into the intuition behind it but generally speaking it functions as follows: The game consists of a n × n lattice on which an agent is placed at ...
0answers
36 views

### Implementing a tic tac toe board in python

This is my attempt at making a class to represent a game board for tic tac toe. I normally hate while loops but I used one because I cant seem to make the ...
1answer
65 views

### Pad a ragged multidimensional array to rectangular shape

For some machine learning purpose, I need to work with sequences with different lengths. To be able to process efficiently those sequences, I need to process them in batches of size ...
1answer
39 views

### Efficient resampling of time series

I'm trying to create an efficient function for re-sampling time-series data. Assumption: Both sets of time-series data have the same start and end time. (I do this in a separate step.) Resample ...
1answer
46 views

### Grid class for games using python

I made this class to eventually create a tic tac toe game. I used numpy which is a first for me. Here it is: ...
0answers
32 views

### Sortings stocks into quantiles based on their signal

This function sorts stocks into quantiles. To do so I used this function that accepts sig_df (dataframe with the timeseries of stocks signal) and number of ...
2answers
118 views

### Positive cumulative sum of difference

I have a water reservoir with input and output rates. I want to determine when the input is exceeding the output by a certain constant. To accomplish this, I need to cumulatively sum all cases where ...
1answer
62 views

### Optimal algorithm to move a a rope from one position to another

I'm an engineer working with a deformable membrane that is attached to actuators. The goal is to move the membrane from one shape to another, without ripping the membrane. This imposes "neighbor ...
3answers
138 views

### Python solution for the N-Queens challenge

Here is my coded solution for the N-queens challenge The n-queens puzzle is the problem of placing n queens on an n×n chessboard such that no two queens attack each other. The program outputs all ...
0answers
63 views

### Optimising Probabilistic Weighted Moving Average (PEWMA) df.iterrows loop in Pandas

I'm implementing the Probabilistic Exponentially Weighted Mean for real time prediction of sensor data in pandas but have issues with optimising the pandas notebook for quick iterations. Is there a ...
0answers
61 views

### Numerical integration in cython

I have a set of nested functions that I need to call multiple times. I know scipy.quad is pretty fast, but I will need to call the integrator recursively and want ...
1answer
57 views

### Gravity simulation using Numpy and Pygame

This is a simple gravity simulator coded in Python 3.7 using Numpy and Pygame. I was wondering if it can be optimized further. Initially I had coded it using pure Python lists, using nested loops to ...
1answer
93 views

### Choosing evenly distributed points from a million points on a sphere

I have $10^5$ to $10^6$ points on a sphere, and want to choose some points from them which are as close as uniformly distributed as possible. For that reason, I do the following: at each step I ...
0answers
168 views

### Population dynamic simulation on biological information maintenance 2

This question is the follow-up to this previous question. Background Using this simulation I investigate a system in which enzymes proliferate in cells. During the replications of enzymes, ...
0answers
55 views

### Find indices using for loop

I should estimate the effect of B fields on particle deflection using $F=V \times B \times Force$. I have a 2D mesh with $n_x$ and $n_y$ which show the number of points in each direction. $B$ ...
0answers
47 views

### Python list operation - merge adjacent cubes into minimum number of shapes

I am hoping to find a way to make the process a lot faster. The lists are made of rows of 6 numbers, i.e. [[float] * 6, ...]. The intent is to pass a list of cube ...
2answers
87 views

### 3D metrics for segmentation evaluation

I am new to programming and I am trying to develop a machine learning approach for image segmentation (https://en.wikipedia.org/wiki/Image_segmentation) and here I want to evaluate the predicted (...
1answer
63 views

### Extract principal components

First, I am aware that this can be done in sklearn - I'm intentionally trying to do it myself. I am trying to extract the eigenvectors from np.linalg.eig to form ...