Geometric medians in reconciliation spaces

In evolutionary biology, it is common to study how various entities evolve together, for example, how parasites coevolve with their host, or genes with their species. Coevolution is commonly modelled by considering certain maps or reconciliations from one evolutionary tree $P$ to another $H$, all of which induce the same map $\phi$ between the leaf-sets of $P$ and $H$ (corresponding to present-day associations). Recently, there has been much interest in studying spaces of reconciliations, which arise by defining some metric $d$ on the set $Rec(P,H,\phi)$ of all possible reconciliations between $P$ and $H$. In this paper, we study the following question: How do we compute a geometric median for a given subset $\Psi$ of $Rec(P,H,\phi)$ relative to $d$, i.e. an element $\psi_{med} \in Rec(P,H,\phi)$ such that $$\sum_{\psi' \in \Psi} d(\psi_{med},\psi') \le \sum_{\psi' \in \Psi} d(\psi,\psi')$$ holds for all $\psi \in Rec(P,H,\phi)$? For a model where so-called host-switches or transfers are not allowed, and for a commonly used metric $d$ called the edit-distance, we show that although the cardinality of $Rec(P,H,\phi)$ can be super-exponential, it is still possible to compute a geometric median for a set $\Psi$ in $Rec(P,H,\phi)$ in polynomial time. We expect that this result could be useful for computing a summary or consensus for a set of reconciliations (e.g. for a set of suboptimal reconciliations).Comment: 12 pages, 1 figur

Unifying Parsimonious Tree Reconciliation

Evolution is a process that is influenced by various environmental factors, e.g. the interactions between different species, genes, and biogeographical properties. Hence, it is interesting to study the combined evolutionary history of multiple species, their genes, and the environment they live in. A common approach to address this research problem is to describe each individual evolution as a phylogenetic tree and construct a tree reconciliation which is parsimonious with respect to a given event model. Unfortunately, most of the previous approaches are designed only either for host-parasite systems, for gene tree/species tree reconciliation, or biogeography. Hence, a method is desirable, which addresses the general problem of mapping phylogenetic trees and covering all varieties of coevolving systems, including e.g., predator-prey and symbiotic relationships. To overcome this gap, we introduce a generalized cophylogenetic event model considering the combinatorial complete set of local coevolutionary events. We give a dynamic programming based heuristic for solving the maximum parsimony reconciliation problem in time O(n^2), for two phylogenies each with at most n leaves. Furthermore, we present an exact branch-and-bound algorithm which uses the results from the dynamic programming heuristic for discarding partial reconciliations. The approach has been implemented as a Java application which is freely available from http://pacosy.informatik.uni-leipzig.de/coresym.Comment: Peer-reviewed and presented as part of the 13th Workshop on Algorithms in Bioinformatics (WABI2013

Fiscal Update, October 5, 2005

The Fiscal Division newsletter, published weekly during session and periodically during the interim

City of Nevada, Independent Auditor's Reports, Basic Financial Statements and Supplemental Information, Schedule of Findings, June 30, 2004

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Interviewing the Client

This paper examines an assignment where students taking either an introductory auditing students or an accounting communications course interview a client to gain an understanding of internal control and the interview process. Students document the results of the interview in a memorandum. The paper provides detailed information regarding the design and implementation of a portion of the internal control system. The three main objectives of the assignment are 1) to provide students with the opportunity to demonstrate, develop, and enhance their communication skills; 2) to convey a realistic picture of the accounting environment; and 3) to familiarize students with a typical responsibility of entry-level accountants

The transition to IFRS: disclosures by Portuguese listed companies

In the context of the CESR and of the Portuguese market regulator recommendations regarding the disclosure of the impacts of the transition to IFRS, this paper analyses the content of those disclosures by Portuguese listed companies. We found a high degree of variability among the disclosure either regarding the qualitative (narrative explanations of transition) or quantitative (reconciliations) disclosures. The results show that the objective of comparability, relevance and understandability stated in CESR’s recommendation were not achieved. Regarding accounting changes, the analysis shows that the reported impacts by companies confirmed expectations based on prior de jure studies on major impacts of changing from Portuguese GAAP to IFRS; these major impacts regard the recognition of intangibles, the accounting treatment of goodwill and financial instruments. Finally, Gray’s (1980) “conservatism” index was computed using the reconciliated profits to IFRS reported by companies. This analysis shows that Portuguese standards are more conservative than IFRS. This study is relevant to several parties: to the market regulators and policy makers in predicting the level of compliance with IFRS and calling attention for the importance of enforcement mechanisms; to the preparers, auditors and users in identifying the most problematic areas of implementation of IFRS.International Accounting, Disclosure, IAS/IFRS, Portugal