# Questions tagged [numpy]

NumPy is the fundamental package for scientific computing with Python.

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26 views

### Why when I increase the standard deviation in the pdf function the graph looks squeezed instead of more dispersed?

So what I am doing is this: ...
17 views

### Combine TFIDF with non-textual features

I am dealing with an email classification problem in which I have email requests coming from different groups of people. I am building a classifier to classify these emails based on historical email ...
21 views

### Estimate joint probability of two dependent variable

I've a dataset created in the following way: The input of the system is a 8 bit binary number ranging from $x_1$= 0000 0000 to $x_N$ = 1111 1111 For every input i've read the output of the system (...
19 views

### Generate random values to mimic skewness

I have a actual set of data where the variables are heavily skewed, both positively and negatively. I need to generate random sample data for the values going forward. The data needs to be similarly ...
14 views

### Q-Exponential distribution in Numpy

I am studying a phenomena, which I know is characterised by the q-exponential distribution, with parameters $c=1$, $q = 1.355$ and $b = 0.524$ in the equation e_{q,b,c}(t) = c(1 + b(q-1)t)^{\frac{1}{...
15 views

### Adding features lowered accuracy score Gaussian Naive Bayes algorithm, Python

I am in third year of university, this simple py program is meant to use the Gaussian Naive Bayes algorithm to create a model and evaluate it. ...
13 views

### Feeding multiple rows of data into ANN [closed]

I've built an ANN from scratch, that works with one row of data with any number of neurons and hidden layers. For the setup I am using 2 hidden layers, 5 neurons (just while building). The network ...
27 views

### Infinitesimal generator of Markov chain using numpy

I am computing the infinitesimal generator of a continuous-time Markov chain from the transition probabilities p. I am following the methodology described here, ...
76 views

### Transforming data for normality with negative values using python

I am working with a data set in a machine learning project, which has lots to negative values. I want to transform the distribution of my data to normal. I tried using numpy.log, but since log is only ...
10 views

### Numpy corrcoef giving different result from manual calculation

I'm trying to calculate a partial correlation matrix for a high dimensional problem. I'm using this paper as a guide. I'm also referencing this function from Pingouin. Starting from the inverse ...
16 views

### Can't Recreate Values for U, S, V from SVD in numpy [duplicate]

To better understand SVD, I'm trying to recreate the values for U, S, and V using straight ...
30 views

44 views

### Outliers of small dataset

I have a python function that takes a list of smaller images boxes (represented as float arrays) and the whole image img in as a ...
28 views

### Different number of Eigen/Singular values from PCA and SVD

My understanding is that a SVD done on a raw data matrix M and a PCA done on its covariance matrix C should return the same eigen/singular values. I have a 2736 x 356 data matrix and am using the ...
304 views

### Fitting Beta Distributions to Data

I am trying to reproduce some beta distribution parameters found in this published paper. I have two data sets, y1 and y2, that ...
19 views

### Proper way of calculating statistics for samples probabilites [closed]

I have 64 samples and for each one of them, I have their probability. I was wondering which is the correct way to find a mean and std for the above-mentioned population. If I do something like: <...
5 views

### Correlation fails on high sampling rate vector

I am trying to find the time shift between two vectors. My function succeeds on randomly generated vectors, but fails on small shifted, high sampling rate vectors. my code: ...
111 views

### Gradient Descent Vectorization with Numpy (1D transpose confusion) [closed]

I'm working through Andrew Ng's original Stanford course and ran into some numpy confusion. Basically, my main question is, if we dot product a 1D array with a 2D array in numpy (and the dimensions ...
25 views

### is it reasonable to consider a plot of 2 separate normal random variables as the geometric representation of a joint probability distribution?

I am plotting 2 normal distribution in Python. if anyone could provide an R version to demonstrate and explain, that would be grateful. ...
1k views

### Array of samples from multivariate gaussian distribution Python

I am trying to build in Python the scatter plot in part 2 of Elements of Statistical Learning. First it is said to generate 10 means mk from a bivariate Gaussian distribution N((1,0)T,I) and ...
183 views

### Efficiently Computing The Beta CDF [duplicate]

I am using numba to JIT compile some looped python functions as part of a larger application. Ideally, everything will run in numba's "no python" mode, such that the loop can be parallelised. One of ...
726 views

### Ridge Regression with Gradient Descent Converges to OLS estimates

I'm implementing a homespun version of Ridge Regression with gradient descent, and to my surprise it always converges to the same answers as OLS, not the closed form of Ridge Regression. This is ...
396 views

### Implementing Lasso Regression in Numpy

I'm doing a little self study project, and am trying to implement OLS, Ridge, and Lasso regression from scratch using just Numpy, and am having problems getting this to work with Lasso regression. ...
42 views

### Rank 1 SVD with constraint on U

I need to perform a particular rank 1 decomposition of a sparse matrix $\mathbf{A} \in \mathbb{R}^{n\times n}$. In particular I am looking for the positive vector $\mathbf{u} \in \mathbb{R}^{+n}$ ...
58 views

### What is the formula for calculation of R_ij in numpy.corrcoef(x, y, rowvar = False)?

The manual does not provide the formula if we pass x and y. I do not understand the matrix I get. Here is my code: ...
26 views

I'm doing PCA (Principal Component Analysis) in Python using the numpys Singular Value Decomposition. Effectively extracting the principal components like so: ...
23 views

### Implement an Intercept T-Test in NumPy

Quick statistical question from an university econ student. In Stata, when you run a linear regression, they perform a t-test of the intercept coefficient to see if it is statistically different from ...
22 views

### Memory considerations with sklearn classfier

I am trying to fit a sklearn.ensemble.RandomForestClassifier. The [docs] explain that a matrix (rows - observations, columns - features). My observations are 700 ...
19 views

### Generating correlated data using numpy while controlling multicollinearity

I am using the following code (adopted from the code in this post). I have no problems with the code. My question is that if with this code I can create or prevent multicollinearity among the ...
1k views

### PCA principal components in sklearn not matching eigen-vectors of covariance calculated by numpy

I was trying to replicate PCA in sklearn's PCA API using numpy using PCA in numpy and sklearn produces different results. I noticed that: eigenvalues are same as the PCA object's explained_variance_ ...
15 views

### Constructing an appropriate null hypothesis?

I have a collection of 20 2D surfaces embedded in 3D. The mean curvature of each surface has been sampled. The number of samples per surface varies from ~700,000 to ~20,000,000. The choice of ...
418 views

### Normalised and “Normal” Cross Correlation giving different lag positions

Using numpy's np.correlate() am trying to find the lag position of two data sets of different length. When I use this operation by its own I find a lag position ...
59 views

### Shifting Data So That When Cross Correlated Lag position is 0

Using Numpy, I am cross correlating two large data sets (of different lengths), as part of a method to compare the similarity of the data. However to take the data onto the next step of the comparison ...
17 views

### Matplotlib: Why would a KNN regression model draw a line through ALL points regardless of K?

Having difficulty doing something very basic: create a random dataset taking on values between -1,1, plot them, and also fit a KNN model to the data and fit it over the data. Using numpy to create the ...
585 views

### Finding the appropriate polynomial fit in Python

Is there a function or library in Python to automatically compute the best polynomial fit for a set of data points? I am not really interested in the ML use case of generalizing to a set of new data, ...
328 views

### How to interpret e.g. pcov returned by numpy.optimize.curve_fit

When doing parameter fits with mathematics frameworks as e.g. numpy, often a covariance matrix is returned. I wonder how to interpret these and if the following is right: The entries of the ...
206 views

TL;DR numpy.gradient calculates the gradient of an ndarray, but I am not clear as to what it is with respect to what original function. An example, (although I ...
82 views

### How to compute the F1 score?

Here is my code: score = metrics.f1_score(y_test[0:], y_pred, pos_label=list(set(y_test))) And here are my dimensions/shapes, which I print before executing the ...
38 views

### Why my perceptron doesn't train well and produces bad results on test data?

I am a newbie in Machine learning and I am writing a small code for Perceptron. This is the first time I am writing code in Python. I have four training data points (X). As they are used for ...
33 views

### Remove individual points and find slope

I am trying to delete one pair of x and y coordinates from a set of 10 data points and get the slope for the other 9 points. How do I go about this issue? Attached herewith is an image of what I am ...
825 views

### python computing likelihood causing exp overflow

I am using numpy to compute the likelihood of a variable $Z$ using numpy. $Z$ is a Bernoulli random variable which has two outcomes $[0,1]$. I compute the log likelihood of observing $Z$ given the ...
320 views

### Discrete Fourier transform of an exponential decay

I have a vector with an exponential decay signal, using Numpy: t=np.arange(128) a=0.1 decay=np.exp(-a*t) I would like to compute the discrete Fourier transform (...
868 views

### Normalization of convolution kernel

I am trying to smooth a noisy one-dimensional physical signal, y, while retaining correspondence between the signal's amplitude and its units. I'm applying a ...
114 views

### Fitting two parallel lines with mutually excluding samples

I have a set of (slightly noisy) data taken from two (or more) curves, but taken either from one or the other curve. As an example, consider this code (in reality, data is noisier, especially in how ...
In his well known paper , Achlioptas showed that Random Projections could be performed with a sparse projection matrix, whose nonzero entries are either $1$ or $-1$. I have noticed that scikit-...