NumPy is the fundamental package for scientific computing with the programming language Python.
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39 views
Computing the weighted centroid dependent on previous row/column
I am working on a project for a Raspberry Pi that requires some image processing.
The aim is to find a white line on a black background by finding the weighted mean in each row/column. However to ...
0
votes
0answers
50 views
Cosine similarity computation
I have a matrix of ~4.5 million vector [4.5mil, 300] and I want to calculate the distance between a vector of length 300 against all the entries in the matrix.
I got some great performance time ...
2
votes
0answers
31 views
Optimize iteration over numpy array with vectorize [closed]
I have the following method which deals with numpy arrays to find the cumulative minimum from each element and its neighbors above:
...
12
votes
0answers
194 views
Backpropagation in simple Neural Network
I've been working on a simple neural network implemented in python. Currently, it seems to be learning, but unfortunately it doesn't seem to be learning effectively. The graph below shows the output ...
3
votes
1answer
55 views
Compressing time series by removing repeated samples
I work on a project with time series data. So there are samples (\$y\$), and each sample has a timestamp (\$x\$). The data will be visualized, but often there are time series which contain samples ...
4
votes
2answers
68 views
Vectorizing a pixel-averaging operation in Numpy
I am reading from a file containing some segments (irregular parcels of the image) and trying to average the entire segment to have one pixel value. This is the code I use:
...
3
votes
0answers
29 views
Speed up a Gibbs sampler with Cython
I have implemented a Gibbs sampler to generate textured images. According to the beta parameters (array of shape(4)), we can generate various textures.
Here is my ...
4
votes
2answers
140 views
Intersection of N lists, or of an N-d array
I often find myself having to do np.intersect1d() multiple times because I need to find the intersection of a number of list like or array like things. So I ended ...
1
vote
2answers
50 views
Generating fractals and space filling curves, using a general function for L-systems
An L-system is a rewriting system that can be used to generate fractals and space filling curves, because of its recursive nature.
Some L-systems for mathematical curves can be found here.
An ...
3
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3answers
104 views
5
votes
2answers
57 views
Python Cartesian Product in a constrained dictonary
I want to calculate the Cartesian product of n copies of a small list, marker=[0,1,2]. I want to use these Cartesian product ...
5
votes
1answer
75 views
Calculating a table of deBroglie wavelengths for various electron energies
Here is the formula for the deBroglie wavelength of an electron versus its kinetic energy:
$$ \lambda(E_k) = h\left/\sqrt{\frac{(E_k+m_eC^2)^2-m_e^2C^4}{C^2}}\right.$$
and here is simple script that ...
3
votes
1answer
54 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'...
2
votes
1answer
31 views
Find signal's maximum peak in window
I have a 9-dimensional signal (as a csv from this Gist) that looks like this:
A signal peaks every 30 steps. I want to get the maximum values of the peaks in that ...
6
votes
1answer
157 views
Python! (Snake)
This is now an Iterative Review.
Next Iteration
Nowhere near a full game yet. Just a basic overview and initialisation of a Snake() class.
Thoughts?
...
1
vote
1answer
55 views
Counts instances for each category for many Matlab files
This is for machine learning. I have 5 matlab files: AWA, REM, S1, S2, SWS.
Each one has 2 arrays: x and y. ...
2
votes
1answer
60 views
Generate a random discrete signal
I currently have this code to generate a discrete signal with random amplitudes, but a fixed frequency:
...
8
votes
1answer
111 views
Monty Hall Optimization in Python 3.5
This is for homework but the deadline is over and I know the implementation is correct because it concurs with the math. At this point I just want to check my implementation for potential ...
4
votes
1answer
35 views
Surface Density Profile
I am trying to compute the surface density profile, given the spherical density profile in 3D for different parameters in order to interpolate and have it as a function of them to use later on for ...
4
votes
1answer
82 views
Conditional removal of columns in sparse matrix
I have a large dataset (78k instances x 490k features) that is loaded as a scipy.sparse.csr_matrix format. From this dataset I want to filter certain features (i.e. ...
5
votes
0answers
90 views
Two versions of Sudoku
I have written two versions of a sudoku solver. Both can solve 9x9 sudoku boards in <200 ms. One of the implementations uses numpy. I am looking for feedback on both, but particularly on why my ...
3
votes
2answers
48 views
Returning a NumPy array (or list) of strings of words repeated N times
I have a list of \$n\$ words, and a corresponding \$m \space x \space n\$ frequency matrix (as a NumPy array). I would like to return a list/array of strings of length \$m\$ where the \$m\$th string ...
4
votes
2answers
69 views
Export data from Python to spreadsheet
I have written the following code to export to data to a spreadsheet with this result:
Please let me know how to improve it.
...
1
vote
1answer
38 views
Mean of combined sublists with different lengths
I have a seemingly simple issue. Consider this list:
a = [[12.0, 5.0, 63.0], [0.1, 2.0, 7.1, 3.0, 2.3, 5.0, 8.4]]
I want to find the mean (using ...
5
votes
0answers
74 views
Computing intersections of a Polyline and a line
I wrote a script to compute / interpolate the nodes of a Polyline at a given latitude, input_lat. It works for my purpose but I am wondering if there is a better, ...
1
vote
1answer
103 views
Sum over selected numpy.ndarray column and write to a file
I am trying to write the sum of selected NumPy array column and write to a file.
The following code snippet is working fine:
...
7
votes
2answers
1k 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 ...
2
votes
2answers
1k views
Plot heat map from csv file using numpy and matplotlib
There's a csv file with format:
x0, y0, v00
x0, y1, v01
...
x1, y0 v10
...
And what I want to do is to plot a heat map, in which at location (x, y) the value v ...
3
votes
1answer
62 views
Scoreboard with score evolution plots using classes
I've very recently started using OOP paradigms for the code in my work (academic research). As an exercise I tried coding this quick scoreboard.
I'm not interested in improving the 'display' part, I ...
4
votes
0answers
130 views
Optimizing the calculation of complex exponential numbers using OpenMP
I am trying to create a function that can either beat numexpr or perform comparably for the vectorized mathematical operation ...
3
votes
2answers
97 views
Assembling edges of a graph
I'm making a neural network that comprises five populations of feature-selective neurons and one population of non-selective neurons. Each neuron in this network receives connections from
c * f * ...
7
votes
2answers
261 views
Histogram of a string
I'm teaching myself Python and when a friend posted this sentence
Only the fool would take trouble to verify that his sentence was
composed of ten a's, three b's, four c's, four d's, forty-six e'...
5
votes
1answer
219 views
Koch snowflake in Python with numpy and pygame
I've drawn a Koch snowflake with Python 3. I'm new to the Python world and would appreciate all feedback on how to make the code more Pythonic as I'm not used to these idioms, styles and modules. All ...
3
votes
1answer
82 views
Normalizing data over a distribution
I have a list X containg the data performed by different users N so the the number of the ...
5
votes
1answer
562 views
k-means clustering algorithm implementation
Here is my personal implementation of the clustering k-means algorithm.
...
2
votes
1answer
262 views
Check if a numpy array contains numerical data
This function serves me as a testing-utility to check if the result is really numeric and sometimes as input-validation if there are a lot of operations before I would find out (with an Exception) if ...
1
vote
1answer
74 views
Finding cointegrated pair with minimal t-score
The function findMinimal() receives a tuple from a list which contains 171 tuples, each of them go into the function one by one and, for each tuple, it searches the ...
3
votes
1answer
54 views
Slicing a big NumPy array
I have a function that takes a four-dimensional NumPy array M and, for each value i of its second index, takes all of M without the i-th "column", evaluates the product over all other columns, and ...
3
votes
1answer
141 views
2
votes
0answers
30 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 ...
2
votes
1answer
54 views
Performance optimization when switching from nested to flat representation (genetic algorithm)
The code below is the core of a Genetic Algorithm (NSGA-II to be precise, without crowding-distance calculation), but I've taken out all the GA-specific parts and made a generic example. I think I've ...
3
votes
1answer
103 views
Project Euler problem #11 - Largest product in a grid
I have recently solved the following Project Euler problem:
In the 20×20 grid below, four numbers along a diagonal line have been marked in red [here bold].
...
1
vote
1answer
25 views
Organizing a Python list of lists as function of number of occurances
I am having a Python list of lists, that I get as an output of python-igraph (membership to clusters). The integers represent an association of a vertex to a ...
5
votes
1answer
269 views
Python Octree Implementation
I'm working with 3D point clouds stored in Numpy arrays. I'd succesfully used the scipy's KDTree implementation for task like k-neighbors search and outlier filtering.
However I wanted to try the ...
1
vote
0answers
83 views
Snell's law using Zoeppritz equation by matrices
I have created the following code to calculate Snell's law angles, based on Zoeppritz equations on complex plane. The code works, seems it is returning valid values, but after all the code just looks ...
2
votes
2answers
253 views
Simulation of 2D elastic balls
Following this SO post and this Wikipedia article, I wrote a Python script to simulate physics of 2D elastic balls.
I define the physical behaviour of each ball in the ...
0
votes
1answer
69 views
Computing logits for a vector and for all vectors in a set
I've had to write two different functions (shown below), but I want to combine the two functions into one. Is there a way to do this?
softmax_a_set() takes a list ...
2
votes
1answer
63 views
Quickly find percentile with high precision
I need to find the percentile where a list of values is higher than a threshold. I am doing this in the context of optimization, so it important that the answer is precise. I am also trying to ...
0
votes
0answers
70 views
Memory efficient alternative passing mostly static variables w/ 1 dynamic variable to an external function (COM) instead of a for loop in Python
Massive data problem, 7/8 variables are repeated 1000 times in a for loop, sending 8 input vectors * 50,000 values per loop for each function call. Only 1 input ...
1
vote
1answer
110 views
Finding the percentile corresponding to a threshold
I need to find which percentile of a group of numbers is over a threshold value. Is there a way that this can be speed up? My implementation is much too slow for the intended application. In case this ...
