# Questions tagged [svd]

Singular value decomposition (SVD) of a matrix $\mathbf{A}$ is given by $\mathbf{A} = \mathbf{USV}^\top$ where $\mathbf{U}$ and $\mathbf{V}$ are orthogonal matrices and $\mathbf{S}$ is a diagonal matrix.

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### Using SVD to write the least squares fitted vector

Elements of statistics p.66 Please I know the least squares solution for $\hat\beta = (X^TX)^{-1}X^Ty$ but I don't know how they were able to get $X\hat\beta= X(X^TX)^{-1}X^Ty = UU^Ty$ These are the ...
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### How to compute the left singular eigenvector matrix (U) from the output of prcomp() for PCA in R?

I am examining the output of the prcomp() function in R for PCA in light of the singular value decomposition equation: $X = U \cdot \Sigma \cdot V^{T}$, where: $X$: ...
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### Singular value decomposition used for dimensionality reduction in brain signal topographic data

I am trying to replicate the localizer method described in this paper (page 4). I am stuck on a step which I don't completely understand, and I would like your input and interpretation to progress. ...
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### Physical interpretation of $U$ and $V$ matrices in SVD

I have a question about the physical interpretation of $U$ and $V$ matrices in SVD. I collect measurements at multiple devices across time are collected into an $m$ × $T$ matrix $M$, where m is the ...
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### Kernel matrix decomposition

I had a look at the sklearn.kernel_approxiamtion.Nystroem implementation, which is also described in this post: Nystroem Method for Kernel Approximation Here, a ...
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### Equal variance along left and right singular vectors?

Please confirm or reject my line of reasoning: Given SVD of $X$: $X_{NxP}=U_{NxP}D_{PxP}V_{PxP}'$, Variance along ith column vector of $U$ is given by $||X'u_i||^2=u'_iXX'u_i=u'_id_i^2u_i=d_i^2$, ...
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### How to predict for test set when training a recommender by decomposing the utility matrix X=UV?

This probably sounds stupid but I don't get the workflow of building a recommending system by the utility matrix: X[i,j] = how much the ith user likes the jth object. For practical issues I refer to ...
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### How does the Zeiger-McEwin & Kung algorithm work for fitting a sum of exponentials?

I am trying to understand this paper fit sum of exponentials but am having a bit of difficulty. Let me go through what I have understood so far. One has a certain time-series data set and want's to ...
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### SVD for a complex data matrix — what is the meaning of the columns of $V$?

I've read this wonderful explanation of SVD, where the writer mentions that the columns of $V$ are the principal directions (Summary, #1). Is this also true when the data matrix $X$ is complex? If I'm ...
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### Computing Pairwise Distances Through PCA or SVD

What should I do to reduce an mxn (m=17, n=650,000) matrix, where m are samples and n are features of these samples, into a matrix of pairwise distances (which I will then use to generate a dendrogram)...
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### Which form of SVD is most commonly in stats/ML (e.g., PCA, least squares)?

SVM comes in several forms: e.g., the full form and the reduced forms https://en.wikipedia.org/wiki/Singular_value_decomposition#Reduced_SVDs. Is there one that is more commonly used in stats? If so, ...
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### Human intuition behind SVD in case of recommendation system

This does not answer my question. I struggled very hard to understand the SVD from a linear-algebra point of view. But in some cases I failed to connect the dots. So, I started to see all the ...
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### How vector projection works behind SVD?

I was reading a blog on mathematical intuition behind SVD. Here, author pointed out three information we get after vector decomposition. The directions of projection — the unit vectors (v₁ and v₂) ...
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### SVD : Why right singular matrix is written as transpose

The SVD is always written as, A = U Σ V_Transpose The question is, Why is the right singular matrix written as V_Transpose? I mean lets say, W = V_Transpose and then write SVD as A = U Σ W SVD Image ...
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### Relationship between the SVD and correlation matrices

I'm reading Data Driven Science and Engineering by Kutz and Brunton to understand more about the SVD. Consider $X = U\Sigma V$, $XX^*$, and $X^*X$ where $X \in \mathbb{R}^{m\times n}$ In particular, ...
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### Penalized Canonical Correlation in R with PMA Module

I am trying to use sparse canonical correlation analysis as implemented in the R PMA package. I'm finding that the correlations output by the package seem slightly inconsistent with the ones you would ...
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### How are eigenvalues/singular values related to variance (SVD/PCA)?

Let $X$ be a data matrix of size $n \times p$. Assume that $X$ is centered (column means subtracted). Then, the $p \times p$ covariance matrix is given by $$C = \frac{X^TX}{n-1}$$ Since $C$ is ...
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### Symbolic Singular Value Decomposition? U,S,V as function of the elements of M [closed]

Suppose we want to compute the SVD of $\mathbf{M} = \begin{bmatrix} m_{11} & m_{12} & m_{13} \\ m_{21} & m_{22} & m_{23} \\ m_{31} & m_{32} & m_{33} \end{bmatrix}$ (...
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### Dimension reduction and get a dataset with the number of features that larger than the minimum of the numbers of samples and features

I'm trying to perform dimension reduction with SVD on an image dataset with the shape of roughly (3000,20000) as you see the number of each sample's features is way larger than the number of samples, ...
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### How to project test data onto new space after using svd on trining data for dimension reduction [duplicate]

I'm working on a dataset of images and i was using the code below to apply dimension reduction to my data set and project the test data onto the new space: ...
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### How to build a recommendation system for users outside of original model data?

I am creating a collaborative filtering model in Python to recommend possible movies a user may like. So, using typical methods in this field, I have a sparse matrix nxm with n users and m movies. ...
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### Moore Penrose Pseudo-Inverse Fast Algorithm in R [closed]

I want to apply Moore Penrose Pseudo-Inverse on my matrix, which is a 20,000 * 20,000 symmetric matrix with rank 19,999. I found ginv() function from the ...
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### Orthonormalization to use closed form Lasso solution

Given the Lasso problem $$min_\beta (Y-X\beta)^\top(Y-X\beta) \quad s.t. \|\beta\|_1\leq\lambda,$$ and assuming that X is orthonormal such that $X^\top X=I$, we know that the closed form solution ...
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### Singular Value Decomposition (SVD) for feature selection

I was reading a paper called "Production Optimization Using Machine Learning in Bakken Shale", and came across an approach I was a bit puzzled by. Unfortunately, the paper is behind a paywall, but I ...
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### Least Square Fitted Vector Through SVD Equals to y

Elements of Statistical Learning, p 66 The SVD of the $N \times p$ matrix $X$ has the form $X = UDV^T$ Here $U$ and $V$ are $N \times p$ and $p \times p$ orthogonal matrices, with the ...
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### Why does this pattern show up so often when doing svd on text data?

A lot of times, I'll get some text data and, as a quick fist step, I'll get a term-frequency matrix, take the first two dimensions of the truncated SVD, and plot it. I very often get a picture that ...
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### Transformation of SVD for latent semantic analysis

General Idea: I'm working through a particular implementation of Latent Semantic Analysis via SVD. Here is some example code. fairly simple: ...
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### Projecting New Data onto Existing Principal Axes

Let $\mathbf{X}$ be a dataset of size $n \times d$, where $n$ is the number of samples (days) and $d$ is the number of variables (daily observations). All observations are taken at the same times each ...
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### What does it mean when PCA does not produce a reduction in dimensionality?

I am a beginner in PCA, I am trying to apply it on a dataset I have. The features are different geometrical parameters with different units and variability, I do standardize the features matrix by ...
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### How to approximate a Hermitian matrix with a transposed cross product of a single matrix?

I have a complex square matrix, and wish to learn latent factors (equally weighted latent factors, so not SVD) from this matrix. Given a Hermitian matrix A of ...
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### Finding the optimal number of latent factors in Symmetric Singular Value Decomposition

Consider symmetric Singular Value Decomposition of a symmetric unitary matrix A into U, D, ...
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### Subtracting PCA projection from original data

I'm trying to implement Anomaly Detection algorythm from this article https://iopscience.iop.org/article/10.1088/1742-6596/1069/1/012072/pdf at my work. So I have big questions for me: Did I ...
Suppose that $X$ has a multivariate normal distribution $X\sim MVN (\mu, \Sigma)$, How can I transform $X$ into $Z$ so that $Z\sim MVN(\mu, I)$ where $I$ is the identity matrix? For instance, ...