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Singular Value Decomposition (SVD) is a decomposition (factorization) of rectangular real or complex matrix into the product of a unitary rotation matrix, a diagonal scaling matrix, and a second unitary rotation matrix.

2 votes

Why is Matlab's SVD faster on skinny matrices than on fat matrices?

(Another related question to which I don't have a good answer is "why doesn't LAPACK's SVD routine DGESVD accept a TRANS parameter, unlike several others?".) …
Federico Poloni's user avatar
6 votes
Accepted

Finding the $i$-th largest eigenvalue of a matrix

No, there is nothing, as far as I know, unless you know approximately the location of these eigenvalues. As for methods that can compute a subset of the spectrum of a matrix, I know only of methods th …
Federico Poloni's user avatar
4 votes

Asymptotic complexity of fixed-rank SVD

You can now compute and SVD of $R$, and use it to piece back the factors with a few matrix products with cost $O(\max(m,n)k^2)$. …
Federico Poloni's user avatar
3 votes
Accepted

Whitening transformation does NOT return a unit covariance matrix

As a final note, as someone who works in numerical linear algebra, I can't avoid pointing out that svd($XX^T$) is not the most numerically stable way to compute the singular values and vectors of $X$, …
Federico Poloni's user avatar
5 votes

My Complex Matrix SVD is Correct according to rule A = USV' but Wrong according to Matlab or...

This should not be possible. $U$ and $V$ may be non-unique in the case where there are repeated singular values, but $s$ must be unique, since it is the sorted list of eigenvalues of $A^*A$ and eigenv …
Federico Poloni's user avatar
10 votes
Accepted

Why are all eigen solvers iterative?

There is simply no closed-form expression in terms of the four operations and radicals for the eigenvalues of a matrix greater than $4\times 4$. This follows from the facts that (1) there are polynomi …
Federico Poloni's user avatar
9 votes
Accepted

Poor SVD reconstruction of singular matrix

Algorithms for the SVD, as more or less every classical linear algebra algorithm based on orthogonal transformations, are normwise backward stable, i.e., it should be guaranteed that $\frac{\|USV^* - A …
Federico Poloni's user avatar
3 votes

accuracy problem for a null space calculation on a sparse rectangular matrix

You mention in a comment that the relative residual norm(Bm*Lrm) / norm(Bm) / norm(Lrm) is of the order of machine precision. So everything is working as intended, it seems. Essentially, the computed …
Federico Poloni's user avatar