Subject: REFEREE'S REPORT Concurrency and Computation:Practice and Experience From: Frédéric Desprez Date: Thu, 18 Oct 2001 08:39:03 +0200 To: "Geoffrey Fox(CandC:PandE Referee Report)" CC: Frédéric Desprez X-UIDL: 7dc6d0e377210000 X-Mozilla-Status: 0001 X-Mozilla-Status2: 00000000 Received: by mailer.csit.fsu.edu (mbox gcfpc) (with Cubic Circle's cucipop (v1.31 1998/05/13) Thu Oct 18 11:38:13 2001) X-From_: fox@mailer.csit.fsu.edu Thu Oct 18 08:44:31 2001 Return-Path: Delivered-To: gcfpc@csit.fsu.edu Received: from dirac.csit.fsu.edu (dirac.csit.fsu.edu [144.174.128.44]) by mailer.csit.fsu.edu (Postfix) with ESMTP id 7CC1123A13 for ; Thu, 18 Oct 2001 08:44:31 -0400 (EDT) Received: from localhost by dirac.csit.fsu.edu (AIX4.2/UCB 8.7) id IAA85366; Thu, 18 Oct 2001 08:44:30 -0400 (EDT) Resent-Message-Id: <200110181244.IAA85366@dirac.csit.fsu.edu> Replied: Thu, 18 Oct 2001 08:44:22 -0400 Replied: Frédéric Desprez Delivered-To: fox@csit.fsu.edu Received: from mask.uits.indiana.edu (mask.uits.indiana.edu [129.79.6.184]) by mailer.csit.fsu.edu (Postfix) with ESMTP id F015123A17 for ; Thu, 18 Oct 2001 02:39:08 -0400 (EDT) Received: from buffalo.ens-lyon.fr (buffalo.ens-lyon.fr [140.77.1.8]) by mask.uits.indiana.edu (8.10.1/8.10.1/IUPO) with ESMTP id f9I6abI27484 for ; Thu, 18 Oct 2001 01:36:37 -0500 (EST) Received: from ens-lyon.fr ([140.77.13.47]) by buffalo.ens-lyon.fr (8.11.6/8.11.2) with ESMTP id f9I6d5r07277; Thu, 18 Oct 2001 08:39:05 +0200 (MET DST) Message-ID: <3BCE7907.D6D57DB0@ens-lyon.fr> Organization: LIP ENS Lyon, INRIA X-Mailer: Mozilla 4.7 [en] (WinNT; U) X-Accept-Language: en MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Resent-To: Geoffrey Fox Resent-Date: Thu, 18 Oct 2001 08:44:30 -0400 Resent-From: Geoffrey Fox Dear Geoffrey, here is my report. Sorry for the delay. Best regards, Frederic ========================================================== REFEREE'S REPORT Concurrency and Computation:Practice and Experience ********** A: General Information Please return to: Geoffrey C. Fox Electronically Preferred gcf@indiana.edu Concurrency and Computation: Practice and Experience Computer Science Department 228 Lindley Hall Bloomington Indiana 47405 Office Phone 8128567977(Lab), 8128553788(CS) but best is cell phone 3152546387 FAX 8128567972 Please fill in Summary Conclusions (Sec. C) and details as appropriate in Secs. D, E and F. B: Refereeing Philosophy We encourage a broad range of readers and contributors. Please judge papers on their technical merit and separate comments on this from those on style and approach. Keep in mind the strong practical orientation that we are trying to give the journal. Note that the forms attached provide separate paper for comments that you wish only the editor to see and those that both the editor and author receive. Your identity will of course not be revealed to the author. C: Paper and Referee Metadata Paper Number Cnnn: C517 Date: Oct 17, 2001 Paper Title: Automatic Determination of Matrix-Blocks Author(s): Victor Eijkhout Referee: Frederic Desprez (and J-Y L'Excellent) Address: LIP, Ecole Nationale Superieure de Lyon, 46, allee d'Italie, 69364 Lyon Cedex 07, France Referee Recommendations. Please indicate overall recommendations here, and details in following sections. reject D: Referee Comments (For Editor Only) The article is light and not completely convincing. The idea to use the "natural" structure of a matrix is attractive; however, the experimentation part does not show that this method is good compared to a method where reordering the matrix would be allowed. I would not accept the article unless the method is proven to be of interest compared to techniques that would allow reordering. This would need a study and comparison with existing methods to define blocks for iterative methods, and the experimentation part should be significantly extended. Also, the presentation needs improvements and the text is not clear in several places. (See parts E and F) E: Referee Comments (For Author and Editor) * The idea to use natural blocks of a matrix, without reordering, to guide an iterative procedure looks attractive and original; however, the experimentation section is disappointing. The comparison with an even split does not bring much because this is clearly a bad approach for the matrix tested. Section 1 says that using the natural blocks of the matrix is useful, but the experiments do not show that this can be better than allowing reordering of the matrix. Therefore in my opinion, the interest of the approach still needs to be proven. For that, the paper should include a part describing existing techniques that aim at defining blocks of a matrix for an iterative method, possibly allowing reordering and a comparison with those should be made. For example, wouldn't a general partitioner working on the adjacency graph of the (symmetrized) matrix provide better blocks at lower cost, possibly better than the splitting called "optimal" ? This would be interesting to study. * The algorithms proposed appear very costly but there might be some simple ways to decrease their costs. For instance in Figure 2, if row segment j is 0 for a given i_0, then a flag(i_0) could be set in order to avoid testing the smaller row segment j again for i > i_0. * The discussions on parallel aspects of the algorithms is not mature. The text should not insist on these aspects because parallel versions are not ready to be implemented/experimented. The focus should be on proving that the method works well, and possibly then on refining the sequential implementation. F: Presentation Changes - The presentation of the algorithms and tables could be improved. - Figures should be centered. - The description of the algorithms (sections 2 and 3) could be clearer. - It would be good to have a state of the art of existing techniques to define blocks and a conclusion showing in details the benefits brought by the new heuristic. More detailed comments follow (lines are for text, excluding tables and figures): p2, l24: "lose us anything" should be reworded. p2, l27: "compressed storage scheme" is not clear. If you mean compressed row storage then it makes sense to use the upper triangular part of the matrix. P2, l-2: "a zero element" -> "a nonzero element" (I think) p3, l1: "spit"->split p3, l6&7: Instead of running the algorithm of figure 2 in parallel for different values of p, couldn't some info from a previous pass with a larger band be reused ? p3, section 3: "or regular domains that have already been subjected to a Cuthill McKee ordering" There is an apparent contradiction. If such an ordering is applied, then as said in section 1, the natural block information from the application is lost. Following the logic, there is then no reason to use a method that does not allow reordering the matrix anymore. If on the other hand it is worth to combine reordering techniques with the natural detection of blocks proposed, then this should be experimented. p3, l-8 to -3: the paragraph is difficult to understand. It supposes that the matrix is distributed in some way but there is no information on this. P4, beg.: It would be useful to recall the mechanics of an alternating Schwarz preconditioner and how convergence may depend on the definition of the blocks and the connections between blocks. P4, l12: "one small of size" -> "a small one of size" P4, l13: "we simulated 8 processors throughout" is not clear. P4, l3: "The is" -> "The matrix is" P5&7, tables 1&2: Since the general splitting gives a better convergence than the "optimal" splitting in table 2, the term "optimal" could be replaced by "natural" or "regular". -------------------------------------------------------------------------------------------------- .