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boost/graph/push_relabel_max_flow::is_flow() bug?
by Arun Bhalla 27 Mar '04

27 Mar '04

Hi, I'm not really a user of Boost, but I've been referring to the Boost Graph Library code for another project. In particular, I've been looking at push_relabel_max_flow.hpp. I was writing a unit test which followed the same ideas of the is_flow() test, and it was failing on what should be a flow network with a valid maximum flow. The code in question: // a is an edge_descriptor if (capacity[a] > 0) if ((residual_capacity[a] + residual_capacity[reverse_edge[a]] != capacity[a]) || (residual_capacity[a] < 0) || (residual_capacity[reverse_edge[a]] < 0)) return false; I contend the test should actually be: // a is an edge_descriptor if (capacity[a] > 0) if ((residual_capacity[a] + residual_capacity[reverse_edge[a]] ! != capacity[a] + capacity[reverse_edge[a]]) || (residual_capacity[a] < 0) || (residual_capacity[reverse_edge[a]] < 0)) return false; I refer to an example network in CLR (1st ed.), p.589. There are several vertices, but I focus on vertices v1 and v2. In this graph, we have capacities c(v1,v2) = 10 c(v2,v1) = 4 and residual capacities cf(v1,v2) = 11 cf(v2,v1) = 3 With the above (original) test, it would fail because 11 + 3 (the sum of residual capacities) != the capacity of either edge. This would hold true if the sum of residual capacities were compared with the sum of capacities. Ordinarily this test would work if reverse_edge[a] has a capacity of 0, which would be the case if the edge (a) is in the flow network, but its reverse is not. I'm not a graph theory expert, though, so I defer to anyone who is. :) Thanks, Arun

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Defining less on member variables/functions
by Chris Jurney 26 Mar '04

26 Mar '04

I've had this same pattern come up 4 or 5 times now, and each time I've been unable to find a stl + boost solution that allowed me to do what I want without writing my own less function. Basically, I want something that will let me do a sort, or define a map on structs or pairs without writing a less that compares the member variable or .first. My last attempt: vector<pair<float, float>> myVector std::sort(myVector.begin(), myVector.end(), _1.first < _2.first); No such luck. It looks like I can do operator * and & on lambda objects, but not access members through them. Is there anything in boost, stl, or elsewhere that lets me not write this: class myLess { bool operator() (pair<float, float> a, pair<float, float>b) {return a.first < b.first;} } Thanks for any help, Chris

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Re: [Boost-users] MAC OS X installation of boost libs
by Michael Short 26 Mar '04

26 Mar '04

Hello I am using MAC OS X 10.3.3. First I done find the bjam tool? Second when I build the bjam tool myself I get the following error. Jamfile:71: in module scope rule unless unknown in module. I think if you could please just give me a quick step by step of what you did to setup the libs with the correct directorys you used then that would probably fix the problems. I did try following the instructions on the page you stated but just did not help. thanks Michael On Tuesday, March 23, 2004, at 09:25PM, James Mastro <jmastro(a)rochester.rr.com> wrote: >On Mar 22, 2004, at 5:12 PM, Michael Short wrote: > >> The only problem is that I am having problems installing and building >> the libs on my MAC OS X system. > >What kind of problems? What version of OS X? I built boost 1.31.0 on >OS X 10.3.2. I think the regex library gave me some problems, but I >believe everything else built OK. > >I just followed the directions here: > >http://www.boost.org/more/getting_started.html > >-jim > > >

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MultiArray questions
by Dr Mark H Phillips 24 Mar '04

24 Mar '04

Hi, I've recently found out about the existence of MultiArray and I am quite impressed! I was thinking of implementing something similar myself but now hopefully I don't have to! However I have a few questions that I'm hoping someone can answer. Question 1 ---------- In the user documentation there is an example which has some example code: for(index i = 0; i != 3; ++i) for(index j = 0; j != 4; ++j) for(index k = 0; k != 2; ++k) A[i][j][k] = values++; Why can't you change the != into <? Ie, do: for(index i = 0; i < 3; ++i) for(index j = 0; j < 4; ++j) for(index k = 0; k < 2; ++k) A[i][j][k] = values++; or can you? This would be more efficient I should think, and requiring that index types be ordered shouldn't be too onerous should it? Question 2 ---------- If I use the built-in "no-frills" C array type to represent a 2-dimensional array in row-major order, then I would access an element (i, j) by doing: a[ &a[0] + i*n + j ] where a is my m by n array. And if I wish to traverse a, in row-major order, I can do: for (int* ip=&(a[0]); ip<&(a[n*m]); ip+=n) { for (int* ijp=&(ip[0]); ijp<&(ip[n]); ++ijp) { visit(ijp); } } These are a very efficient ways of doing things, but it lacks somewhat in ease-of-generalization and in readbility. This is where the MultiArray library is useful. But do I lose in efficiency by going to MultiArray? Ie, in the simple case where base is 0, stride is 1, and when we traverse in row-major order, is the MultiArray library smart enough to do compile-time optimizations to generate code which is as efficient as the above? I am guessing that this sort of approach is what the Blitz++ library does?? Question 3 ---------- Is it possible to construct a new multi_array/multi_array_ref/const_multi_array_ref from an array_view by doing a deep copy of the view? A view is a nice way of looking at different parts of a MultiArray object in a readable way, but sometimes you might wish to turn this view into a more-efficiently represented object. Is this easy to do in the MultiArray library? Question 4 ---------- Sometimes you might have an object starts off being mostly accessed in row-major order, so you want a representation which works efficiently for this use. But down the track you might wish to change to mostly column-major access. Does MultiArray provide easy ways to transform from one underlying representation to another? Thanks, Mark Phillips.

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RE: [Boost-users] boost::filesystem::exists() & GetfileAttributesA
by Ben Hutchings 24 Mar '04

24 Mar '04

Sebastian Orfino <sorfino(a)lanacion.com.ar> wrote: > I am experiencig a problem with exists() and its Windows > implementation with GetFileAttributes API. I am using exists() prior > to the scan of a directory to see if it exists; the fact is that on > W2K (just tested it on that OS) after a day or two > GetFileAttributesA() returns INVALID_FILE_ATTRIBUTES but the path > does exists (it is a UNC-style path). > After a restart of the app, all works fine. <snip> It couldn't possibly be related to this bug, could it: <http://support.microsoft.com/default.aspx?scid=kb;en-us;325929>? I know that that talks about Windows XP clients and NT 4 servers but MS does not always test thoroughly whether a bug found in one version of a product exists in other versions. The bug is supposed to be fixed in Windows XP SP2, by the way.

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It always show compiler limitation when I use boost.python to wrap a class under MSVisualStudio .Net
by Shunming Fang 24 Mar '04

24 Mar '04

Hello, guys, I try build my c++ lib as python modules using boost.python, when compile one big class, it always show compiler limit( my ram already update to 1.5 GB) while the class can be smoothly build on other platforms like SGI, Linux(RAM 512 MB+). I don't know why? I already upgrade my MSVS .net to 2003Version, Anybody know How I can get around this problems? Thank you very much __________________________________ Do you Yahoo!? Yahoo! Finance Tax Center - File online. File on time. http://taxes.yahoo.com/filing.html

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Boost error on Red Hat Linux 7.4
by Jonathan Arnold 24 Mar '04

24 Mar '04

I'm trying to build the latest (1.31.0) Boost libraries for the first time on a Red Hat Linux 7.4, gcc 2.96 system. It seems to build all the libs and such correctly, but I get the following error trying to build the test programs: gcc-C++-action bin/boost/libs/test/build/libboost_test_exec_monitor.so/gcc/debug/shared-linkable-true/test_tools.o /home/jdarnold/boost_1_31_0/libs/test/build/../src/test_tools.cpp: In method `void boost::test_toolbox::detail::print_log_value<char>::operator() (ostream &, char)': /home/jdarnold/boost_1_31_0/libs/test/build/../src/test_tools.cpp:194: parse error before `__ctype_b' /home/jdarnold/boost_1_31_0/libs/test/build/../src/test_tools.cpp:205: confused by earlier errors, bailing out set -e g++ -c -Wall -ftemplate-depth-100 -DBOOST_TEST_NO_AUTO_LINK=1 -g -O0 -fno-inline -fPIC -I"bin/boost/libs/test/build" -I "/home/jdarnold/boost_1_31_0" -o "bin/boost/libs/test/build/libboost_test_exec_monitor.so/gcc/debug/shared-linkable-true/test_tools.o" "/home/jdarnold/boost_1_31_0/libs/test/build/../src/test_tools.cpp" /usr/bin/objcopy --set-section-flags .debug_str=contents,debug "bin/boost/libs/test/build/libboost_test_exec_monitor.so/gcc/debug/shared-linkable-true/test_tools.o" What is going wrong here? Is my version of F++ too old? Thanks in advance. -- Jonathan Arnold (mailto:jdarnold@buddydog.org) Daemon Dancing in the Dark, a FreeBSD weblog: http://freebsd.amazingdev.com/blog/

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Cannot use BGL & boost::format together under VS2003
by Alexeev Gleb 24 Mar '04

24 Mar '04

Hi all! The following simple sample doesn't compile on VC++ .NET 2003: #include <iostream> #include <boost/format.hpp> // without the following line everything's ok #include <boost/graph/adjacency_list.hpp> int main(){ std::cout << boost::format("%d, %s") % 5 % "some text"; return 0; } -- Best regards, Alexeev Gleb mailto:alexeev_gleb@hotbox.ru

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boost/graph - induced subgraph
by Matthew Galati 24 Mar '04

24 Mar '04

Is it possible to find the minimum spanning tree of an induced subgraph? vector< graph_traits<Graph>::vertex_descriptor > vd; typedef subgraph< Graph > SubGraph; SubGraph & inducedG = subG.create_subgraph(vd.begin(), vd.end()); Here is the example I am looking at: induced verts: 1 2 3 4 5 7 Original Graph: 0 <--> 1 2 5 7 1 <--> 0 3 5 7 2 <--> 0 3 4 5 3 <--> 2 1 4 5 4 <--> 2 3 5 6 5 <--> 0 1 2 3 4 6 7 6 <--> 4 5 7 7 <--> 0 1 5 6 Induced Graph: 1 <--> 3 5 7 2 <--> 3 4 5 3 <--> 2 1 4 5 4 <--> 2 3 5 5 <--> 1 2 3 4 7 7 <--> 1 5 So, the "create_subgraph" seems to be working fine. But, when I run kruskals with: vector<graph_traits < SubGraph >::edge_descriptor> spanning_tree; kruskal_minimum_spanning_tree(inducedG, back_inserter(spanning_tree)); for (vei = spanning_tree.begin(); vei != spanning_tree.end(); ++vei) { pair<int,int> ij = incident(*vei, inducedG); int edge_index = e_index[*vei]; cout << "e_index: " << edge_index << " : " << ij.first << " " << ij.second << endl; I get a spanning tree of just 4 edges (while the subgraph has 6 vertices). Also, how does the edge_index of the subgraph correspond to the original graph? For example, edge (4,1) is not in the original graph, but it shows up in my spanning tree. Spanning Tree: e_index: 3 : 2 0 e_index: 7 : 4 0 e_index: 4 : 3 1 e_index: 8 : 4 1 Thanks, Matthew -- Matthew Galati ISE Lehigh University IBM Service Parts Solutions 610.758.4042 (Office) 610.882.0779 (Home) magh(a)lehigh.edu, magal11(a)us.ibm.com http://sagan.ie.lehigh.edu/mgalati/

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boost-sandbox socket and boost 1.31.0?
by Robert Helgesson 23 Mar '04

23 Mar '04

Howdy, I'm wondering regarding the socket library found in boost-sandbox. Will it be updated to function nicely with the latest Boost release? The problem seems to be that boost::default_iterator_policies and boost::iterator_adaptor no longer work like the socket library expect. Regards -- / Robert Helgesson |-- rycee(a)home.se --\ \-- GPG Key ID: 41E95A5B --| http://www.rycee.cx/ /

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