Maths lecturers in denial about their own maths practice? A case of teaching matrix operations to undergraduate students

This case study provides evidence of an apparent disparity in the way that certain mathematics topics are taught compared to the way that they are used in professional practice. In particular, we focus on the topic of matrices by comparing sources from published research articles against typical undergraduate textbooks and lecture notes. Our results show that the most important operation when using matrices in research is that of matrix multiplication, with 33 of the 40 publications which we surveyed utilising this as the most prominent operation and the remainder of the publications instead opting not to use matrix multiplication at all rather than offering weighting to alternative operations. This is in contrast to the way in which matrices are taught, with very few of these teaching sources highlighting that matrix multiplication is the most important operation for mathematicians. We discuss the implications of this discrepancy and offer an insight as to why it can be beneficial to consider the professional uses of such topics when teaching mathematics to undergraduate students

Rapid Mixing of the Switch Markov Chain for 2-Class Joint Degree Matrices

The switch Markov chain has been extensively studied as the most natural Markovchain Monte Carlo approach for sampling graphs with prescribed degree sequences. In this work westudy the problem of uniformly sampling graphs for which, in addition to the degree sequence, jointdegree constraints are given. These constraints specify how many edges there should be between twogiven degree classes (i.e., subsets of nodes that all have the same degree). Although the problem wasformalized over a decade ago, and despite its practical significance in generating synthetic networktopologies, small progress has been made on the random sampling of such graphs. In the case of onedegree class, the problem reduces to the sampling of regular graphs (i.e., graphs in which all nodeshave the same degree), but beyond this very little is known. We fully resolve the case of two degreeclasses, by showing that the switch Markov chain is always rapidly mixing. We do this by combininga recent embedding argument developed by the authors in combination with ideas of Bhatnagar et al.[Algorithmica, 50 (2008), pp. 418--445] introduced in the context of sampling bichromatic matchings

Connected realizations of joint-degree matrices

We study a restriction of the classic degree sequence graphic realization problem studied by Erdős, Gallai, Havel, and Hakimi, namely the joint-degree matrix graphic realization problem. Here, in addition to the degree sequence, a joint degree matrix is given, the (i,j)th element of which specifies the exact number of edges between vertices of degree di and vertices of degree dj. The decision and construction versions of the problem have a relatively straightforward solution. In this work, however, we focus on the corresponding connected graphic realization version of the problem. We give a necessary and sufficient condition for a connected graphic realization to exist, as well as a polynomial time construction algorithm that involves a novel recursive search of suitable local graph modifications. As a byproduct, we also suggest an alternative polynomial time algorithm for the joint-degree matrix graphic realization problem that never increases the number of connected components of the graph constructed

Connected realizations of joint-degree matrices

We study a restriction of the classic degree sequence graphic realization problem studied by Erdős, Gallai, Havel, and Hakimi, namely the joint-degree matrix graphic realization problem. Here, in addition to the degree sequence, a joint degree matrix is given, the (i,j)th element of which specifies the exact number of edges between vertices of degree di and vertices of degree dj. The decision and construction versions of the problem have a relatively straightforward solution. In this work, however, we focus on the corresponding connected graphic realization version of the problem. We give a necessary and sufficient condition for a connected graphic realization to exist, as well as a polynomial time construction algorithm that involves a novel recursive search of suitable local graph modifications. As a byproduct, we also suggest an alternative polynomial time algorithm for the joint-degree matrix graphic realization problem that never increases the number of connected components of the graph constructed