All posts by Christoph Conrads

Talk: Working Remotely with Secure Shell, Grid Engine, and Screen

On Monday, February 23, 2015, I gave a talk in the tools seminar at my university about three tools that are useful when working remotely on another computer and that I use a lot:

Regarding secure shell, I explained how to use several of the programs that are part of OpenSSH. Grid Engine is a software suite for cluster management and you have to use it in order to submit jobs to the cluster of the mathematics department at my university. Screen is a window manager for terminals and offers--among other things--persistent shell sessions. Screen is not a program for remote computer access but I felt that that persistent shell sessions integrate nicely with remote computer work.

You can download the presentation slides here (PDF).

Talk: Introducing Git

On October 20, 2014 Cornelia Gamst and me gave a short talk on Git (Wikipedia) in the tools seminar at the Berlin Institute of Technology. The target audience were people who did not know what a version control system is or who had not used Git before hence we gave reasons why revision control is a good thing and why we use Git for it. The Git introduction itself was brief and included only the basic workflow though we had the opportunity to demonstrate some of the more powerful Git abilities during the hands-on exercise.

The slides are available from the website of the tools seminar.

Performance and Accuracy of xPTEQR

xPTEQR is a LAPACK function for the computation of the  eigendecomposition of a symmetric positive definite tridiagonal matrix. I compare the performance and accuracy of xPTEQR to the other symmetric eigensolvers in LAPACK 3.5.0.

In layman’s terms, there are several algorithms available on a computer that calculate the eigenvectors and eigenvalues of matrices with special properties (symmetric, positive definite, tridiagonal). xPTEQR is the name of the computer implementation of one of those algorithms and I am not aware of any measurements with it. In this blog post I compare xPTEQR in terms of speed and accuracy to other good algorithms. In the figures below, xPTEQR can be found under the label "SVD" (xPTEQR is the name of the implementation, SVD is the algorithm). Moreover, in every figure it holds that lower is better.

Continue reading Performance and Accuracy of xPTEQR


Yesterday I bought an SSL certificate and changed my password so that I can securely log into this blog.

I want every reader of this blog to benefit from the available encryption and to that end the blog software forwards all HTTP connections to HTTPS from now on.