| 1. |
- Larsson, Torbjörn, et al.
(författare)
-
Ergodic results and bounds on the optimal value in subgradient optimization
- 1996
-
Ingår i: Operations Research Proceedings 1995. - 9783540608066 ; , s. 30-35
-
Konferensbidrag (refereegranskat)abstract
- Subgradient methods are popular tools for nonsmooth, convex minimization, especially in the context of Lagrangean relaxation; their simplicity has been a main contribution to their success. As a consequence of the nonsmoothness, it is not straightforward to monitor the progress of a subgradient method in terms of the approximate fulfilment of optimality conditions, since the subgradients used in the method will, in general, not accumulate to subgradients that verify optimality of a solution obtained in the limit. Further, certain supplementary information, such as convergent estimates of Lagrange multipliers, is not directly available in subgradient schemes. As a means for overcoming these weaknesses of subgradient optimization methods, we introduce the computation of an ergodic (averaged) sequence of subgradients. Specifically, we consider a nonsmooth, convex program solved by a conditional subgradient optimization scheme (of which the traditional sub gradient optimization method is a special case) with divergent series step lengths, which generates a sequence of iterates that converges to an optimal solution. We show that the elements of the ergodic sequence of subgradients in the limit fulfill the optimality conditions at this optimal solution. Further, we use the convergence properties of the ergodic sequence of subgradients to establish convergence of an ergodic sequence of Lagrange multipliers. Finally, some potential applications of these ergodic results are briefly discussed.
|
|
| 2. |
- Larsson, Torbjörn, et al.
(författare)
-
Ergodic results in subgradient optimization
- 1996
-
Ingår i: Nonlinear Optimization and Applications. - 9780306453168 ; , s. 229-248
-
Konferensbidrag (refereegranskat)abstract
- Subgradient methods are popular tools for nonsmooth, convex minimization, especially in the context of Lagrangean relaxation; their simplicity has been a main contribution to their success. As a consequence of the nonsmoothness, it is not straightforward to monitor the progress of a subgradient method in terms of the approximate fulfilment of optimality conditions, since the subgradients used in the method will, in general, not accumulate to subgradients that verify optimality of a solution obtained in the limit. Further, certain supplementary information, such as convergent estimates of Lagrange multipliers, is not directly available in subgradient schemes. As a means for overcoming these weaknesses of subgradient optimization methods, we introduce the computation of an ergodic (averaged) sequence of subgradients. Specifically, we consider a nonsmooth, convex program solved by a conditional subgradient optimization scheme (of which the traditional subgradient optimization method is a special case) with divergent series step lengths, which generates a sequence of iterates that converges to an optimal solution. We show that the elements of the ergodic sequence of subgradients in the limit fulfill the optimality conditions at this optimal solution. Further, we use the convergence properties of the ergodic sequence of subgradients to establish convergence of an ergodic sequence of Lagrange multipliers. Finally, some potential applications of these ergodic results are briefly discussed.
|
|
| 3. |
|
|
| 4. |
- Larsson, Torbjörn
(författare)
-
How open can a government be? : the Swedish experience
- 1998
-
Ingår i: Openness and transparency in the European Union. - Maastricht : European institute of public administration. - 9067791164 ; , s. 39-52
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)
|
|
| 5. |
|
|
| 6. |
- Larsson, Åke, 1958, et al.
(författare)
-
Measurements on and modelling of capacitor-connecting transients on a low-voltage grid equipped with two wind turbines
- 1995
-
Ingår i: International Conference on Power System Transients (IPST'95), Lisbon, Portugal, September 3-7, 1995. Proceedings pp. 184-188.
-
Konferensbidrag (refereegranskat)abstract
- Capacitor connecting transients on a low-voltage grid equipped with two wind turbines are measured and calculated. As the phase-compensating capacitors of the wind turbines are connected, a large current peak, sometimes reaching twice the rated current, occurs. The damping of the transients is strongly influenced by skin and proximity effects.
|
|
| 7. |
|
|
| 8. |
- Norgren, L, et al.
(författare)
-
Endovaskulär teknik vid aortaaneurysm. Lovande alternativ till öppen kirurgi
- 1998
-
Ingår i: Läkartidningen. - 0023-7205. ; 95:6, s. 508-512
-
Tidskriftsartikel (refereegranskat)abstract
- The article consists in a presentation of endovascular surgery for abdominal aortic aneurysm repair in 23 cases. Two cases required conversion to open surgery, but the procedure could be completed in the remaining 21 cases, with a current duration of follow-up of up to 30 months. There was early leakage in one case, and late leakage in five cases. Late conversion has been necessary in three instances, and supplementary endovascular measures have been required in a further two instances. All complications have occurred in those cases operated during the first half of the study period. Modification of the endoprosthesis used and increasing skill have reduced both operation time and the complication rate. Intensive care is no longer required, and the median duration of hospitalisation is three days. Follow-up with magnetic resonance imaging has yielded new and important information.
|
|
| 9. |
|
|
| 10. |
|
|
