Algorithms for subgraph complementation to some classes of graphs

For a class $\mathcal{G}$ of graphs, the objective of \textsc{Subgraph Complementation to} $\mathcal{G}$ is to find whether there exists a subset $S$ of vertices of the input graph $G$ such that modifying $G$ by complementing the subgraph induced by $S$ results in a graph in $\mathcal{G}$. We obtain a polynomial-time algorithm for the problem when $\mathcal{G}$ is the class of graphs with minimum degree at least $k$, for a constant $k$, answering an open problem by Fomin et al. (Algorithmica, 2020). When $\mathcal{G}$ is the class of graphs without any induced copies of the star graph on $t+1$ vertices (for any constant $t\geq 3$) and diamond, we obtain a polynomial-time algorithm for the problem. This is in contrast with a result by Antony et al. (Algorithmica, 2022) that the problem is NP-complete and cannot be solved in subexponential-time (assuming the Exponential Time Hypothesis) when $\mathcal{G}$ is the class of graphs without any induced copies of the star graph on $t+1$ vertices, for every constant $t\geq 5$

Incompressibility of H-Free Edge Modification Problems: Towards a Dichotomy

Given a graph G and an integer k, the H-free Edge Editing problem is to find whether there exist at most k pairs of vertices in G such that changing the adjacency of the pairs in G results in a graph without any induced copy of H. The existence of polynomial kernels for H-free Edge Editing (that is, whether it is possible to reduce the size of the instance to k^O(1) in polynomial time) received significant attention in the parameterized complexity literature. Nontrivial polynomial kernels are known to exist for some graphs H with at most 4 vertices (e.g., path on 3 or 4 vertices, diamond, paw), but starting from 5 vertices, polynomial kernels are known only if H is either complete or empty. This suggests the conjecture that there is no other H with at least 5 vertices were H-free Edge Editing admits a polynomial kernel. Towards this goal, we obtain a set ? of nine 5-vertex graphs such that if for every H ? ?, H-free Edge Editing is incompressible and the complexity assumption NP ? coNP/poly holds, then H-free Edge Editing is incompressible for every graph H with at least five vertices that is neither complete nor empty. That is, proving incompressibility for these nine graphs would give a complete classification of the kernelization complexity of H-free Edge Editing for every H with at least 5 vertices. We obtain similar result also for H-free Edge Deletion. Here the picture is more complicated due to the existence of another infinite family of graphs H where the problem is trivial (graphs with exactly one edge). We obtain a larger set ? of nineteen graphs whose incompressibility would give a complete classification of the kernelization complexity of H-free Edge Deletion for every graph H with at least 5 vertices. Analogous results follow also for the H-free Edge Completion problem by simple complementation

Scale and impact of the illegal leopard skin trade for traditional use in southern Africa

While leopards (Panthera pardus) currently occupy the most extensive geographic range of all large felids, they are also suffering the highest rate of current range loss amongst large terrestrial carnivores. This is primarily because most leopards still range outside of formally protected areas where they are exposed to the full suite of anthropogenic threats affecting carnivores including habitat loss, prey depletion, conflict with humans, and commercial harvest for body parts. The extensive use of leopard derivatives among traditional healers, royalty, and culturo-religious groups poses a known but poorly understood threat to leopards. Sociopolitical sensitivities surrounding cultural identity and the illegality of much of this use have impeded an objective assessment of both the drivers and impacts of this threat. Through a multi-disciplinary approach, this thesis describes the drivers of illegal leopard skin trade among a significant portion of traditional users in South Africa, quantifies the extent of this trade across the southern African region and assesses its impact on local leopard populations. Together these findings seek to address the lack of conservation- and policy-relevant data regarding the impact and scale of the trade for traditional use in South Africa. Followers of the recently established ‘Shembe' Church, with its estimated membership of over four million in South Africa, represent the foremost culturo-religious users of illegal leopard skins in the world. Following the introduction of a faux skin alternative, I used longitudinal surveys to explore the drivers of authentic skin desirability and possession amongst faux skin recipients. While demand for authentic skins decreased, and faux alternatives were generally considered satisfactory, 27% still expressed a desire for an authentic skin, and 15% had acquired one in the three years since receiving their faux skin. Both desiring and having obtained an authentic skin were best explained by improved economic status and the perceived weakness of law enforcement. The combined demand of all Shembe followers cannot be sustained by the estimated extant leopard population of South Africa, and it is predicted that traders must be sourcing leopards from surrounding range states to meet local demands. To investigate this, I created a genetic reference database of leopards across southern Africa (1,452 individuals) and using DNA-based assignment tests, inferred the geographic origins of illegally traded skins sourced within southern Africa. Smoothed continuous assignment techniques revealed leopard source ‘hotspots' in southwestern Zimbabwe, southern Mozambique and along the eastern borders of South Africa confirming suspicions that the illegal leopard skin trade for traditional use in South Africa is transnational. A similar distribution of leopard source populations was identified from leopard parts obtained in traditional wildlife markets and a large-scale confiscation from a single trader. Together, this suggests the regional trade in leopard parts has been syndicated with predictable harvesting and trade routes into the South African consumer market. Genotyping across all trade samples (237 individuals) revealed a clear bias towards males despite reported sex-ratios being female-biased for natural free-ranging populations. To understand the ecological cost of this sex-biased exploitation of leopards, I compared the spatial, genetic, and demographic data of two South African leopard populations with markedly different histories of anthropogenic mortality. Home-range overlap, parentage assignment, and spatio-genetic autocorrelation showed that extensive historical exploitation, linked to Shembe and other traditional trade, has reduced subadult male dispersal, thereby facilitating opportunistic male natal philopatry. The resultant kinclustering in males is comparable to that of females in the well-protected reserve and has promoted localised inbreeding. Together these results demonstrate novel evidence linking significant ecological consequences to an underestimated, transnational, and syndicated illegal leopard skin trade driven by demand for traditional and religious use in South Africa. These findings are translatable to all leopard populations threatened by exploitation and emphasise the importance of long-term monitoring of leopard populations within protected areas and improving management interventions to mitigate these effects. Interventions such as anti-poaching can be focussed on the ‘hotspots' identified in this study while protected area management should prioritise the maintenance of dispersal corridors to promote in situ recovery of exploited populations. Lastly, demand reduction strategies such as the continued provisioning of suitable alternatives, together with improved education and increased enforcement, are essential to addressing the growing culturo-religious demand for leopard products contributing to the illegal harvest and trade in this iconic large predator. Success will depend on finding the balance between an improved transnational policy which effectively conserves wild leopard populations and maintaining respect for cultural practice

How to do things with things

Humans have always done things with things. It’s at the very origin of who we are as a species: we’ve gone from being bipedal homonins to people who live in complex societies by making rocks into tools. Things can serve a practical function, but they also carry cultural and symbolic meaning: they can tell our personal stories, allow us to connect with each other, and be the outer manifestations of our inner lives. The things we use in our every day lives, by implying a set of actions we can take when interacting with them, participate in shaping our reality: all things contain a set of implied behaviors, rules, customs, morals and beliefs. How to do things with things is an invitation to look at things as clues with which to investigate reality, and to then go ahead and make new things to invent new realities. If our culture, norms and sense of self are embedded in our things, there’s good news: they are all malleable. We can take things apart and put them back together to look at ourselves from a new perspective. We can (literally) objectify any concept or idea to try it on for size. We can make things that allow people to try entirely new and unexpected behaviors and ideas. Doing things with things is a practice of performativity; it looks at everything around us—from the clothes we wear, to the tools we use and the spaces we inhabit—as a set of messages, stories, and behaviors. In doing so, it’s an invitation to experience and engage with complex ideas and concepts in a way that is not abstract but, instead, embodied. If we can wrestle with the inter-personal, behavioral, socio-psychological and historical aspects of being human by literally interacting with them, we can actively participate in making new versions of all of them and maybe, in the process, become new more-multidimensional humans

Counterfactual Memorization in Neural Language Models

Modern neural language models that are widely used in various NLP tasks risk memorizing sensitive information from their training data. Understanding this memorization is important in real world applications and also from a learning-theoretical perspective. An open question in previous studies of language model memorization is how to filter out "common" memorization. In fact, most memorization criteria strongly correlate with the number of occurrences in the training set, capturing memorized familiar phrases, public knowledge, templated texts, or other repeated data. We formulate a notion of counterfactual memorization which characterizes how a model's predictions change if a particular document is omitted during training. We identify and study counterfactually-memorized training examples in standard text datasets. We estimate the influence of each memorized training example on the validation set and on generated texts, showing how this can provide direct evidence of the source of memorization at test time.Comment: NeurIPS 2023; 42 pages, 33 figure

Beasts of Flight

Beasts of Flight is a set of thirteen short stories connected by themes of personal impotence and the dysfunction of sexual relationships. Some stories are bizarre. The title piece, “Beasts of Flight,” explores systemic hatred and fear through the eyes of a talking parrot. In “I Should Exit My Home When the Costume Party Causes Paralysis of the Brain,” the host of a Halloween party is frozen by the mask of one of his guests. “The Joytime Killbox” details a city’s obsession with staring down the the barrel of a loaded gun. Crossing into sacrilege, “The Book of Smote,” is a subversive take on Old Testament storytelling. Other stories display the inherent strife of relationships using piercings, airplanes, a couple’s movie night, and an impromptu lunch at a fast food restaurant. “My Roberta,” “Rough Air,” “Walking Dogs,” and “Cheri,” all focus on sexual conflict and marital breakdown. The stories “Fallen Timbers,” “USS Flagg,” and “What to Say ff Anything to a Child in the Speedway Bathroom” examines the unexpected repercussions of doing a good deed. While “Homecoming” and “Coetzee Comes to Dinner” illustrate that even the best families have their problems

Beasts of Flight

Beasts of Flight is a set of thirteen short stories connected by themes of personal impotence and the dysfunction of sexual relationships. Some stories are bizarre. The title piece, “Beasts of Flight,” explores systemic hatred and fear through the eyes of a talking parrot. In “I Should Exit My Home When the Costume Party Causes Paralysis of the Brain,” the host of a Halloween party is frozen by the mask of one of his guests. “The Joytime Killbox” details a city’s obsession with staring down the the barrel of a loaded gun. Crossing into sacrilege, “The Book of Smote,” is a subversive take on Old Testament storytelling. Other stories display the inherent strife of relationships using piercings, airplanes, a couple’s movie night, and an impromptu lunch at a fast food restaurant. “My Roberta,” “Rough Air,” “Walking Dogs,” and “Cheri,” all focus on sexual conflict and marital breakdown. The stories “Fallen Timbers,” “USS Flagg,” and “What to Say ff Anything to a Child in the Speedway Bathroom” examines the unexpected repercussions of doing a good deed. While “Homecoming” and “Coetzee Comes to Dinner” illustrate that even the best families have their problems