Linearly convergent adjoint free solution of least squares problems by random descent

We consider the problem of solving linear least squares problems in a framework where only evaluations of the linear map are possible. We derive randomized methods that do not need any other matrix operations than forward evaluations, especially no evaluation of the adjoint map is needed. Our method is motivated by the simple observation that one can get an unbiased estimate of the application of the adjoint. We show convergence of the method and then derive a more efficient method that uses an exact linesearch. This method, called random descent, resembles known methods in other context and has the randomized coordinate descent method as special case. We provide convergence analysis of the random descent method emphasizing the dependence on the underlying distribution of the random vectors. Furthermore we investigate the applicability of the method in the context of ill-posed inverse problems and show that the method can have beneficial properties when the unknown solution is rough. We illustrate the theoretical findings in numerical examples. One particular result is that the random descent method actually outperforms established transposed-free methods (TFQMR and CGS) in examples

Der Todesfall im Wasser im Untersuchungsgut des Instituts für Rechtsmedizin Greifswald - Umstände, Befunde, Besonderheiten

Der Todesfall im Wasser gilt als sehr vielgestaltiger Sachverhalt innerhalb der forensischen Pathologie und stellt deshalb für den Rechtsmediziner eine Herausforderung dar. Zur Feststellung der Todesursache Ertrinken werden in der Literatur verschiedene innere und äußere Ertrinkungszeichen beschrieben, die durch rechtsmedizinische Zusatzuntersuchungen ergänzt werden können. Andere Befunde geben Anhalt für einen Aufenthalt des Leichnams im Wasser. Alle Zeichen stehen jedoch unter mutmaßlicher Beeinflussung durch zahlreiche Faktoren, die die Aussagekraft der Befunde einschränken. Ziel der Untersuchung war es, Todesfälle im Wasser exemplarisch anhand des Obduktionsgutes des Instituts für Rechtsmedizin Greifswald zu charakterisieren, um Erkenntnisse für die rechtsmedizinische Praxis abzuleiten. Dabei sollten die häufigsten Todesumstände herausgearbeitet, erhobene Sektionsbefunde im Kontext der Literatur eingeordnet, und mögliche Beeinflussungsfaktoren identifiziert werden. Dafür wurden die Sektionsprotokolle aller Todesfälle im Wasser im Zeitraum von 1997 bis 2017 gesichtet und systematisch ausgewertet. In der Untersuchung stellte sich heraus, dass von den dominierenden akzidentellen Todesumständen insbesondere alkoholisierte, junge Männer betroffen waren. Frauen hatten zum Todeszeitpunkt durchschnittlich ein höheres Lebensalter erreicht und bei ihnen waren Suizide überrepräsentiert. Die Ertrinkungsraten im Senium waren ebenfalls beachtlich. Diese Altersgruppe könnte bei Vorfällen im Wasser durch (kardiale) Vorerkrankungen und Multimedikation zusätzlich bedroht sein, da der Ertrinkungsvorgang dadurch wahrscheinlich beschleunigt wird. Ferner ließ sich in der Untersuchung aufzeigen, dass nur ein äußerer Schaumpilz (beobachtet unmittelbar nach Bergung des Leichnams) mit hinreichender Signifikanz exklusiv beim Tod durch Ertrinken auftrat. Für alle anderen untersuchten Ertrinkungszeichen, die zusätzlich durch Faktoren wie Reanimation, verlängertes postmortales Intervall und Fäulnis beeinflusst wurden, muss eine eingeschränkte Spezifität für die Diagnostik des Ertrinkungstodes angenommen werden. Letztlich sind eine hohe Expertise und die Nutzung aller diagnostischen Möglichkeiten bei der Aufklärung von Todesfällen im Wasser entscheidend. Diese Erfahrung kann durch die regelmäßige Sektion derartiger Todesfälle gesteigert werden.Death in water is a challenging issue in forensic pathology due to its manifoldness. To determine a death by drowning, various internal and external signs of drowning are described in the literature, which can be supplemented by additional forensic examinations. Other findings indicate that the body has been in the water. However, all signs are under suspected influence by numerous factors limiting their significance and evidence. The aim of the study was to characterize death in water based on the autopsy material of the Institute of Legal Medicine Greifswald to derive knowledge for forensic practice. The most common circumstances of death had to be worked out, observed autopsy findings had to be set in context to the forensic literature and possible influencing factors had to be identified. For this purpose, the autopsy protocols of all deaths in water in the period from 1997 to 2017 were reviewed and systematically evaluated. In the study, we found out that the dominating accidental circumstances of death mainly affected drunk, young men. On the other side, women had reached a higher age at the time of death and suicides were overrepresented in their group. The drowning rates in the senium were also remarkable. This older age group could be additionally threatened by (cardiac) pre-existing morbidities and multimedication in case of an incident in water, as these are likely accelerating the drowning process. Furthermore, the study revealed that only a complete formation of external foam (observed immediately after recovery of the corpse) occurred exclusively in cases of death by drowning. For all other drowning signs examined, which were additionally influenced by factors such as resuscitation, prolonged postmortem interval and putrefaction, a limited specificity for the diagnosis of death by drowning must be assumed. Ultimately, a high level of expertise and the use of all diagnostic opportunities in the investigation of deaths in water are crucial. This experience can be enhanced by the frequent autopsy of these cases

Macromorphological findings in cases of death in water: a critical view on “drowning signs”

Death in water is a challenging issue in forensic pathology since from natural death to homicide all circumstances of death in water are conceivable. Therefore, the correct interpretation of all abnormal autopsy findings is important. In order to determine a death by drowning, numerous internal and external signs of drowning are already described. However, these are supposed to be influenced by various factors reducing their significance and evidence. Moreover, the autopsy of water corpses often reveals further pathological findings that should not be underestimated for determining the cause of death. The aim of this study was to set frequencies of the observed drowning signs in context to the forensic literature and to identify possible influencing factors. In this study, we observed that pathological organ changes of the cardiovascular system were significantly more common in corpses after shortened (atypical) drowning processes than in classical drowned victims. Furthermore only a complete formation of external foam, immediately after the corpse's recovery, was exclusively found in drowning victims. All other drowning signs were either also observed in non-drowning deaths in water or no information could be provided with reasonable assurance. In addition, many of the examined drowning signs were negatively affected by prolonged postmortem intervals, putrefaction, or resuscitation attempts. It can be concluded from our analysis that morbidity is an important factor in deaths in water. Morbidity can support a death by drowning in case of incidents in water. For the examined drowning signs, no high diagnostic certainty could be observed. Nevertheless, these findings can increase their diagnostic value-if forensic physicians take influencing factors into consideration