257 research outputs found
A parallelizable algorithmic framework for solving large scale multi-stage stochastic mixed 0-1 problems under uncertainty
Preprint submitted to Computers & Operations Researchmulti-stage stochastic mixed 0-1 optimization, nonsymmetric scenario trees, implicit and explicit nonanticipativity constraints, splitting variable and compact representations, scenario cluster partitioning
A note on the implementation of the BFC-MSMIP algorithm in C++ by using COIN-OR as an optimization engine
The aim of this technical report is to present some detailed explanations in order to help to understand and use the algorithm Branch and Fix Coordination for solving MultiStage Mixed Integer Problems (BFC- MSMIP). We have developed an algorithmic approach implemented in a C++ experimental code that uses the optimization engine COmputational INfrastructure for Operations Research (COIN-OR) for solving the auxiliary linear and mixed 0-1 submodels. Now, we give the computational and implementational descrip- tion in order to use this open optimization software not only in the implementation of our procedure but also in similar schemes to be developed by the users.nonanticipativity constraints, cluster partitioning, COIN-OR library, branch-and-fix coordination, multi-stage stochastic mixed 0-1 programming
Scenario Cluster Lagrangian Decomposition in two stage stochastic mixed 0-1 optimization
In this paper we introduce four scenario Cluster based Lagrangian Decomposition (CLD) procedures for obtaining strong lower bounds to the
(optimal) solution value of two-stage stochastic mixed 0-1 problems. At each iteration of the Lagrangian based procedures, the traditional aim
consists of obtaining the solution value of the corresponding Lagrangian dual via solving scenario submodels once the
nonanticipativity constraints have been dualized. Instead of considering a splitting variable representation over the set of scenarios, we propose to decompose the model into a
set of scenario clusters. We compare the computational performance of
the four Lagrange multiplier updating procedures, namely
the Subgradient Method, the Volume Algorithm, the Progressive Hedging
Algorithm and the Dynamic Constrained Cutting Plane scheme
for different numbers
of scenario clusters and different dimensions of the original
problem. Our computational experience shows that
the CLD bound and its computational effort depend on the number of
scenario clusters to consider. In any case, our results show that the CLD procedures outperform the traditional LD scheme for single
scenarios both in the quality of the bounds and computational effort. All the procedures have been implemented in a C++ experimental
code. A broad computational experience is reported on a test of
randomly generated instances by using the MIP solvers COIN-OR and CPLEX for the auxiliary mixed 0-1
cluster submodels, this last solver within
the open source engine COIN-OR. We also give computational evidence of
the model tightening effect that the preprocessing techniques, cut
generation and appending and parallel computing tools have in
stochastic integer optimization. Finally, we have observed that the
plain use of both solvers does not provide the optimal solution of
the instances included in the testbed with which we have experimented but
for two toy instances in affordable elapsed time. On the other hand the proposed
procedures provide strong lower bounds (or the same solution
value) in a considerably shorter elapsed time for the quasi-optimal
solution obtained by other means for the original stochastic problem
On solving two stage stochastic linear problems by using a new approach, Cluster Benders Decomposition
The optimization of stochastic linear problems, via scenario analysis, based on Benders decomposition requires to appending feasibility and/or optimality cuts to the master problem until the iterative procedure reaches the optimal solution. The cuts are identified by solving the auxiliary submodels attached to the scenarios. In this work, we propose a so-called scenario cluster decomposition approach for dealing with the feasibility cut identification in the Benders method for solving large-scale two stage stochastic linear problems. The scenario tree is decomposed into a set of scenario clusters and tighter feasibility cuts are obtained by solving the auxiliary submodel for each cluster instead of each individual scenario. Then, this scenario cluster based scheme allows us to define tighter feasibility cuts that yield feasible second stage decisions in reasonable time consuming. Some computational experience by using the free software COIN-OR is reported to show the favorable performance of the new approach over traditional Benders decomposition.This research has been partially supported by the projects ECO2008-00777/ECON from the Ministry of Education and Science, PLANIN, MTM14087-C04-01 from the Ministry of Science and Innovation, Grupo de Investigación IT-347-10 from the Basque Government, and the project RIESGOS CM from the Comunidad de Madrid, Spain
Independence in CLP Languages
Studying independence of goals has proven very useful in the context of logic programming. In particular, it has provided a formal basis for powerful automatic parallelization tools, since independence ensures that two goals may be evaluated in parallel while preserving correctness and eciency. We extend the concept of independence to constraint logic programs (CLP) and
prove that it also ensures the correctness and eciency of the parallel evaluation of independent goals. Independence for CLP languages is more complex than for logic programming as search space preservation is necessary but no longer sucient for ensuring correctness and eciency. Two
additional issues arise. The rst is that the cost of constraint solving may depend upon the order constraints are encountered. The second is the need to handle dynamic scheduling. We clarify these issues by proposing various types of search independence and constraint solver independence, and show how they can be combined to allow dierent optimizations, from parallelism to intelligent
backtracking. Sucient conditions for independence which can be evaluated \a priori" at run-time are also proposed. Our study also yields new insights into independence in logic programming languages. In particular, we show that search space preservation is not only a sucient but also a necessary condition for ensuring correctness and eciency of parallel execution
Versatile Graphene-Based Platform for Robust Nanobiohybrid Interfaces
Technologically useful and robust graphene-based interfaces for devices
require the introduction of highly selective, stable, and covalently bonded
functionalities on the graphene surface, whilst essentially retaining the
electronic properties of the pristine layer. This work demonstrates that highly
controlled, ultrahigh vacuum covalent chemical functionalization of graphene
sheets with a thiol-terminated molecule provides a robust and tunable platform
for the development of hybrid nanostructures in different environments. We
employ this facile strategy to covalently couple two representative systems of
broad interest: metal nanoparticles, via S-metal bonds, and thiol-modified DNA
aptamers, via disulfide bridges. Both systems, which have been characterized by
a multi-technique approach, remain firmly anchored to the graphene surface even
after several washing cycles. Atomic force microscopy images demonstrate that
the conjugated aptamer retains the functionality required to recognize a target
protein. This methodology opens a new route to the integration of high-quality
graphene layers into diverse technological platforms, including plasmonics,
optoelectronics, or biosensing. With respect to the latter, the viability of a
thiol-functionalized chemical vapor deposition graphene-based solution-gated
field-effect transistor array was assessed
Evaluation of Tree Species for Biomass Energy Production in Northwest Spain
This work was funded by the TRIBIONOR Project (Reference CTQ2013-45155-R) and the coal mining company HUNOSA GROUP supported by the HUNOSA CHAIR at the University of Oviedo (Project Reference SV-17-HUNOSA-1). The authors acknowledge the helpful co-operation of Hunosa staff in this study. The TRIBIONOR Project (CTQ2013-45155-R) is funded by the National Program for Research, Development and Innovation in Society Challenges, within the framework of the National Plan for Scientific and Technical Research and Innovation 2013–2016 from the State Research Agency (Ministry of Economy, Industry and Competitiveness), co-financed with FEDER Funds. The authors gratefully acknowledge the Government of the Principality of Asturias for supporting Ana Álvarez with a fellowship within the Severo Ochoa Program.Peer reviewedPublisher PD
Intraductal papillary mucinous neoplasms (IPMN) of the pancreas: clinico-pathologic results
Background: intraductal papillary mucinous neoplasm
(IPMN) shows a series of lesions which evolve from benign lesions
–adenoma– to invasive carcinoma.
Aim: to analyze the clinical and pathological results of 15 patients
diagnosed of IPMN, and surgically treated according to the
guidelines of International Consensus Conference.
Material and methods: a retrospective analysis of 15 patients
surgically treated between March 1993 and September
2009, according to the International Consensus recommendation.
Demographic, diagnostic tools, surgical report, pathologic
database and actuarial survival were analyzed with a follow-up
from one and a half month through nine years.
Results: 6 patients underwent pancreaticoduodenectomies,
4 total pancreatectomies, 2 body or central pancreatectomies, 2 partial
pancreatectomies (enucleation) and 1 distal pancreatectomy.
A morbidity of 46 and 0% hospital mortality were assessed, with
a median length hospital stay of 10 days. In five cases, the IPMN
was combined type (both main and branch pancreatic ducts involved)
in four main duct-type and branch duct-type in the another
six as well. Several atypia (IPMN carcinoma in situ) was
observed in 2 patients and invasive carcinoma with negative
lymph nodes was identified in 3 patients. A patient without invasive
carcinoma died at 66 months of follow-up for pancreas adenocarcinoma.
The actuarial survival up to recurrence or death
was 105,133 months with a range of follow-up from 1 month
and a half until 9 years.
Conclusions: IPMN main duct or mixed type warrants complete
resection due to its incidence of invasive carcinoma or precursor
lesions of malignancy as well. Due to its multifocal pattern,
patients should be followed in long-term surveillance. The management
of asymptomatic IPMN type branch less than 3 cm is
controversial
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