Error in the Slides?

Question

Dear SC team,

I think I found an error in the slides - on slide 2-53 it says that we should maximize U. But at that point U is defined as the Identity matrix, so that this won't have much of an effect. I presume this was intended to be A?

Best Regards,

Kevin Iselborn

PS: I presume we are supposed to write in English right?

Answer 1

This is indeed a typo – thanks for pointing it out. The idea is of course to find the maximum pivot element below the diagonal in the k-th column of $A$. So you are exactly right with your presumption.

(It may be mildly interesting why this typo happened: an earlier version of the slide detailed a variant of the algorithm that sets $U=A$ initially and then works only on $U$. This allows for a more compact formulation, that is however harder to understand. So for didactic reasons, I changed it to the less compact version and missed this line in the process.)

PS: Let's keep with the entire site and stick to English.