# 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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### Singular matrix - but SVD works - what does the eigenvalues mean? Find I the “dependent” lines?

please can I ask a bit stupid question? I have a complex matrix A as a set of equations. I wanted to find the solution of Ax=b where b is vector of right-hand side. So I have called zgetrf on A (does ...
152 views

### FFT - function only in sine series? Can be done with MKL / Lapack? [duplicate]

please can I ask, how one can make from function sine series (Fourier transform) with MKL? I can do "normal" exponential FFT with MKL (Lapack of course), how can I say that I want only sine series? ...
405 views

### LAPACK - singular matrices - what does the positive integer info mean?

please can you help me with my code - I use Lapack to solve complex matrix (quite biq) and do it in two steps: I call zgetrf (LU factorization) and then ...
4k views

### Threaded OpenBlas benchmark slower than system blas?

I'm not sure if I did something wrong or if I just didn't understand the concept of an optimized BLAS. I'm a FEM engineer trying to optimize my setup on a small cluster computer (six nodes). I'm ...
171 views

### Understanding Inner blocking size in lapack/plasma

I could not get accurate description that aids to my understanding of inner blocking size parameter that is used in many LAPACK routines(such as DGEQRT, DLARFB). Thanks
2k views

### Magma vs. Plasma

I'm having a difficult time understanding the difference between the linear algebra packages MAGMA and PLASMA from just a quick glance. It looks like MAGMA is oriented towards GPU's and vector ...
3k views

### What are the fastest available implementations of BLAS/LAPACK or other linear algebra routines on GPU systems?

nVidia, for example, has CUBLAS, which promises 7-14x speedup. Naively, this is nowhere near the theoretical throughput of any of nVidia's GPU cards. What are the challenges in speeding up linear ...
296 views

### Dense generalized hermitian indefinite eigenvalue problem

Lapack contains a driver routine to solve dense generalized Hermitian positive definite eigenvalue problems of the form $Ax=\lambda Bx$, where $A$ and $B$ are both Hermitian, and $B$ is positive ...
5k views

### BLAS/LAPACK subroutine to add two matrices with different offsets and leading dimensions

I currently searching for a subroutine from BLAS or LAPACK which realizes the following operation A = alpha*A + beta * B where A and B have different leading ...
854 views

### Does PETSc ever make use of LAPACK libraries for sparse matrix math?

Does compiling PETSc with an external BLAS/LAPACK library significantly affect performance on sparse matrices, or does it only use those libraries for dense matrix math?
124 views

### Efficient computation of the extension of a linear basis to completion when the basis is almost complete (ideally using LAPACK routines)

I have a $p \times n$ matrix $B$ (where $n < p$) with orthonormal columns and would like to find a numerically efficient way to extend this matrix to get a complete $p$-dimensional orthonormal ...
8k views

### Understanding how Numpy does SVD

I have been using different methods to calculate both the rank of a matrix and the solution of a matrix system of equations. I came across the function linalg.svd. Comparing this to my own effort of ...
3k views

### What is the corresponding LAPACK function behind Matlab [Q,R,E]=qr(A)?

I currently trying to cheaply compute a good rank estimate for a matrix $A$. Therefore I compute a columnt pivoting QR decompostion using [Q,R,E]=qr(A) in ...
2k views

### Why isn't my Matrix-Vector Multiplication Scaling?

Sorry for the long post but I wanted to include everything that I thought was relevant in the first go. What I want I am implementing a parallel version of Krylov Subspace Methods for Dense Matrices. ...
5k views

### How do I use ScaLapack/PBLAS for Matrix-Vector Multiplication?

After going to all possible "Introductions" to ScaLapack, I still can't understand how to carry out a simple PDGEMV operation using it. Here is what I must do : ...
4k views

### How does LAPACK solve tridiagonal systems and why?

In my project I have to solve a couple of tridiagonal matrices at every time step, so it is crucial to have a good solver for those. I did my own implementation, just the classical way to do it ...
381 views

### Easily accessible scientific code that uses LAPACK

I would like to analyze some well-used scientific codes that make heavy use of LAPACK. I.e. I'm looking for codes that both spend a lot of time within LAPACK functions and use LAPACK non-trivially (i....
I'm just getting tucked into fortran 95 for some quantum mechanics simulations. Honestly, I've been spoiled by Octave so I've taken matrix exponentiation for granted. Given a (small, $n\leq 36$) skew-...