On the Minimal Displacement Vector of the Douglas-Rachford Operator

The Douglas-Rachford algorithm can be represented as the fixed point iteration of a firmly nonexpansive operator. When the operator has no fixed points, the algorithm's iterates diverge, but the difference between consecutive iterates converges to the so-called minimal displacement vector, which can be used to certify infeasibility of an optimization problem. In this paper, we establish new properties of the minimal displacement vector, which allow us to generalize some existing results

OSQP: An Operator Splitting Solver for Quadratic Programs

We present a general-purpose solver for convex quadratic programs based on the alternating direction method of multipliers, employing a novel operator splitting technique that requires the solution of a quasi-definite linear system with the same coefficient matrix at almost every iteration. Our algorithm is very robust, placing no requirements on the problem data such as positive definiteness of the objective function or linear independence of the constraint functions. It can be configured to be division-free once an initial matrix factorization is carried out, making it suitable for real-time applications in embedded systems. In addition, our technique is the first operator splitting method for quadratic programs able to reliably detect primal and dual infeasible problems from the algorithm iterates. The method also supports factorization caching and warm starting, making it particularly efficient when solving parametrized problems arising in finance, control, and machine learning. Our open-source C implementation OSQP has a small footprint, is library-free, and has been extensively tested on many problem instances from a wide variety of application areas. It is typically ten times faster than competing interior-point methods, and sometimes much more when factorization caching or warm start is used. OSQP has already shown a large impact with tens of thousands of users both in academia and in large corporations

Tahikardija u novorođenčeta s enterovirusnom infekcijom

Enterovirus infections are common in the neonatal period. Newborns are at a higher risk of severe disease including meningoencephalitis, sepsis syndrome, cardiovascular collapse, or hepatitis. The mechanism of heart failure in patients with enterovirus infection remains unknown. Early diagnosis may help clinicians predict complications in those infants initially presenting with severe disease. An 11-day-old male newborn was admitted to our neonatal intensive care unit because of tachycardia and crises of cyanosis. His elder brother had febrile illness. The newborn was cyanotic, in respiratory distress, with tachycardia, low blood pressure and prolonged capillary refilling time. Limb pulse oximeter was around 85%. During the first day of hospitalization, the newborn had one febrile episode. Laboratory data: elevated transaminases, markers of inflammation negative, all bacterial cultures negative. Enterovirus RNA was detected in blood sample. Other blood findings were without significant abnormalities. Electrocardiogram showed tachycardia, with narrow QRS complexes (atrial tachycardia) and heart rate up to 280/min. In order to convert the rhythm, the patient was administered adenosine and amiodarone. In the further course of hospitalization, the patient was in good general condition, eucardiac and eupneic. Newborns with tachycardia and a family history of febrile illness should be suspected to have enterovirus infection. Enterovirus infection is a highly contagious and potentially life-threatening infection if not detected early. The use of sensitive molecular-based amplification methods offers potential benefits for early diagnosis and timely treatment.Enterovirusne infekcije su uobičajene u neonatalnom razdoblju. Novorođenčad su pod većim rizikom za teške oblike bolesti, uključujući meningoencefalitis, sindrom sepse, kardiovaskularni kolaps ili hepatitis. Mehanizam zatajenja srca u bolesnika s enterovirusnim infekcijama ostaje nepoznat. Rana dijagnoza može pomoći kliničarima da predvide komplikacije na početku u dojenčadi s teškom bolešću. Muško novorođenče staro 11 dana primljeno je u našu jedinicu intenzivne neonatalne skrbi zbog tahikardije i krize cijanoze. Njegov stariji brat imao je febrilnu bolest. Novorođenče je bilo cijanotično, u respiracijskom distresu, uz tahikardiju, nizak krvni tlak i produženo kapilarno punjenje. Pulsna oksimetrija je bila oko 85%. Tijekom prvog dana hospitalizacije novorođenče je imalo jednu febrilnu epizodu. Laboratorijski nalazi su pokazali povišene transaminaze, negativne parametre upale i negativne sve bakterijske kulture. Enterovirusna RNA je otkrivena u uzorku krvi. Ostali nalazi krvi bili su bez značajnih odstupanja. Elektrokardiogram je pokazao tahikardiju s uskim kompleksima QRS (atrijska tahikardija) i srčanom frekvencijom do 280/min. Radi pretvorbe ritma bolesnik je dobio adenozin i amjodaron. U daljnjem tijeku hospitalizacije bolesnik je bio dobrog općeg stanja, eukardičan i eupnoičan. Kod novorođenčadi s tahikardijom i podacima o febrilnosti kod drugih članova obitelji treba posumnjati na enterovirusnu infekciju. Enterovirusna infekcija je vrlo zarazna i potencijalno opasna za život ako se ne otkrije na vrijeme. Osjetljive molekularne metode nude potencijalne prednosti za rano otkrivanje i pravodobno liječenje

Povezanost inzulinu sličnog faktora rasta tip 1 i intrauterinog rasta

Insulin-like growth factor 1 (IGF-1) is a regulator of intrauterine growth, and circulating concentrations are reduced in intrauterine growth-restricted fetuses. The aim of our study was to investigate the relationship between IGF-1 levels in newborns and intrauterine growth, expressed as birth weight (BW). The research was designed as a cross-sectional study. The study included 71 premature newborns, gestational age (GA) ≤33 weeks. Quantitative determination of IGF-1 was performed in the 33rd post-menstrual week (pmw) to make the measurements more comparable. We used an enzyme-bound immunosorbent test for quantitative determination of IGF-1. Our results showed the mean IGF-1 level in premature newborns in 33rd pmw to be 23.1±4.56 (range 15.44-39.75) μg/L. There was no difference in IGF-1 values between male (23.1±4.98 μg/L) and female (23.1±4.87 μg/L) newborns. Tere was no significant difference in the average IGF-1 levels between male and female newborns with BW 50th percentile for GA either (p>0.50). Only BW <33rd percentile newborns had a statistically significantly lower IGF-1 level compared to newborns with greater BW. Based on our results, it is concluded that serum IGF-1 level reflects intrauterine growth only in BW <33rd percentile newborns. This fact could be used for further therapeutic purposes.Inzulinu sličan faktor rasta (IGF-1) je jedan od čimbenika koji utječu na intrauterini rast. Serumske razine IGF-1 su smanjene u fetusima s intrauterinim zastojem rasta. Cilj našega istraživanja bio je ispitati odnos između razine IGF-1 u nedonoščadi i intrauterinog rasta izraženog kao porođajna težina (PT). Istraživanje je provedeno kao presječna studija. U studiju je bilo uključeno 71 nedonošče gestacijske dobi (GD) ≤33 tjedna. Kvantitativno određivanje IGF-1 provedeno je u 33. postmenstruacijskom tjednu (pmt) radi bolje usporedivosti rezultata. Za kvantitativno određivanje IGF-1 rabili smo enzimski imunosorbentni test. Naši rezultati pokazali su da je srednja razina IGF-1 u nedonoščadi u 33. pmt iznosila 23,1±4,56 (raspon 15,44-39,75) μg/L. Nije bilo razlike u vrijednostima IGF-1 između muške (23,1±4,98 μg/L) i ženske (23,1±4,87 μg/L) nedonoščadi. Također nije bilo značajne razlike u srednjim razinama IGF-1 između nedonoščadi s PT 50. percentila za GD (p>0,50). Nedonoščad s niskom PT (<33. percentila) imala su statistički značajno nižu razinu IGF-1. Na temelju naših rezultata može se zaključiti da serumska razina IGF-1 odražava intrauterini rast samo u nedonoščadi male PT (<33. percentila), što bi mogao biti koristan podatak za buduću uporabu IGF-1 u terapijske svrhe

GPU Acceleration of ADMM for Large-Scale Quadratic Programming

The alternating direction method of multipliers (ADMM) is a powerful operator splitting technique for solving structured convex optimization problems. Due to its relatively low per-iteration computational cost and ability to exploit sparsity in the problem data, it is particularly suitable for large-scale optimization. However, the method may still take prohibitively long to compute solutions to very large problem instances. Although ADMM is known to be parallelizable, this feature is rarely exploited in real implementations. In this paper we exploit the parallel computing architecture of a graphics processing unit (GPU) to accelerate ADMM. We build our solver on top of OSQP, a state-of-the-art implementation of ADMM for quadratic programming. Our open-source CUDA C implementation has been tested on many large-scale problems and was shown to be up to two orders of magnitude faster than the CPU implementation

Online Computation of Terminal Ingredients in Distributed Model Predictive Control for Reference Tracking

A distributed model predictive control scheme is developed for tracking piecewise constant references where the terminal set is reconfigured online, whereas the terminal controller is computed offline. Unlike many standard existing schemes, this scheme yields large feasible regions without performing offline centralized computations. Although the resulting optimal control problem (OCP) is a semidefinite program (SDP), an SDP scalability method based on diagonal dominance is used to approximate the derived SDP by a second-order cone program. The OCPs of the proposed scheme and its approximation are amenable to distributed optimization. Both schemes are evaluated using a power network example and compared to a scheme where the terminal controller is reconfigured online as well. It is found that fixing the terminal controller results in better performance, noticeable reduction in computational cost and similar feasible region compared to the case in which this controller is reconfigured online

Work verification of the energy steam boiler evaporator in the Power plant 'Kostolac B'

U okviru Elektroprivrede Srbije 1991. godine puštena je u rad Termoelektrana 'Kostolac B' snage 2 × 350 MW. Na osnovu dosadašnjih ispitivanja cevnog sistema parnog kotla utvrđeno je da se on nalazi u 'lošem' stanju. Njegovi najugroženiji delovi su isparivačke grejne površine. S obzirom da postoje oblasti u isparivaču koje su se češće oštećivale, zbog čega je parni kotao ispadao iz pogona, neophodno je utvrditi razloge zbog kojih je dolazilo do tih oštećenja. Da bi se locirala ugrožena područja isparivača, sproveden je detaljan hidraulički proračun. Takođe je izvršen termički proračun parnog kotla u celini, s obzirom da se isparivač nalazi i u zoni konvektivnih grejnih površina. Utvrđivanjem najugroženije lokacije isparivača - horizontalni deo nosećih cevi, omogućeno je da se pri kapitalnom remontu izvrše određene rekonstrukcije u smislu promene njihovog ugla nagiba, što bi u krajnjem obezbedilo sigurniji rad, kako isparivača tako i kotla u celini.Within Electric Power Utility of Serbia 1991, a thermal power plant 'Kostolac B', power 2 × 350 MW, started. Based on the examination of steam boiler pipe system, it is confirmed that it is in a 'bad' shape. Its most jeopardized parts are evaporating heating surfaces. Considering that there are areas within the evaporator that suffered more damage, wherefore the steam boiler is out of production, it is necessary to settle the reasons for those damages. In order to locate the jeopardized areas of the evaporator, we carried out a detailed hydraulic calculation. A thermal calculation of steam boiler was also carried out, considering that the evaporator is also located in the convective heating surfaces part. By settling the most jeopardized evaporator locations - a horizontal part of support tubes, it was enabled to make certain reconstructions during the capital repair, in regard of changing their inclination angle, which would provide safer work of the evaporator, and steam boiler as a whole