# Questions tagged [lapack]

LAPACK (Linear Algebra PACKage) is a commonly used library of subroutines for numerical linear algebra tasks, including solutions of linear sets of equations, linear least squares, eigenvalue problems, and singular value decomposition. LAPACK routines may be used with fortran, C and relatives and a variety of other languages.

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### MATLAB ordschur producing different results from Lapack's dtrsen in Simulink

My question is very similar to the one previously posted here. I'm using the same MATLAB code for embedding Lapack functions into my code, which I also compiled with Mingw64. The main difference is ...
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### Use of scipy.linalg.cython_lapack.dgbsv in cython script

I was working into accellerating a solver for baded matrix using cython. The base case is the following pure python code : ...
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### 2x2 complex symmetric eigendecomposition - LAPACK subroutine CLAESY

Asking here because I searched the LAPACK user forums and found nothing. I have a problem that requires the computation of the eigendecomposition $A=A^T=Q \Lambda Q^T$ for the 2x2 complex symmetric ...
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### Matrix Diagonalization and Computational Requirements

I have some questions about diagonalizing matrices. My interest lies in computing all eigenvalues of a given matrix. To avoid wasting time and improve my research efficiency, I want to understand the ...
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### Weird runtime behavior of scipy.linalg.solve_triangular and trtrs

I want to understand the time complexity of scipy.linalg.solve_triangular, which calls trtrs from LAPACK under the hood, so I ...
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### What is the correct way of computing $LL^T$ in packed format with blas/lapack

I have a triangular matrix stored in packed format (ie $L$). I need to compute $LL^T$ (not the decomposition, just the multiplication). What would be the preferred way of computing this with blas/...
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### Why is it that SVD routines on nearly square matrices run significantly faster than if the matrix was highly non square?

In Python / Matlab, if you run a routine for SVD on a significantly non-square matrix, X, such as X.shape = (2,15000) you will ...
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### Fast weighted vector inner product x*A*y with BLAS/LAPACK

Is there a way to compute the weighted vector inner product xAy with vectors x and y and Matrix A using BLAS/LAPACK while avoiding additional allocations or overwriting the inputs? I'm happy with ...
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### Using Sundials CVODE in MATLAB

I'm currently using ode15s to solve a set of stiff differential equations. I am trying to use the MATLAB profiler to understand the section of the ode solver code which calls BLAS routines. Since the ...
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### Reordering eigenvalues in Schur factorization - MATLAB ordschur and LAPACK dtrsen not producing the same results

Disclaimer: I previously posted this on SO, but though it would be more relevant for scicomp. The original post has been deleted. I have been trying to recreate the functionality provided by MATLABs <...
1 vote
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### Conditioning and Stability of generalized eigenvalue problem

The (generalized) eigenvalue problems with a multiple eigenvalue are the ill-posed ones. I have two questions that should be simple for experts: (1) Is the eigenvalue problem much more sensitive to ...
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### Eigenvalues of diagonal plus rank-one

I need to compute an eigendecomposition of an $n\times n$ matrix $$D + c vv^\top = Q\Lambda Q^\top \tag{1}$$ in MATLAB, where $D$ is a real diagonal matrix, $c$ is a scalar, and $v$ is a real vector....
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### Parallelize pseudo inverse of a matrix using Lapacke

I am currently using the protocol described in https://stackoverflow.com/questions/55599950/computation-of-pseidoinverse-with-svd-in-c-using-blas-and-lapacke to compute the pseudo inverse of a matrix. ...
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