/* -*- mode: C++; indent-tabs-mode: nil; -*-

  *

  * This file is a part of LEMON, a generic C++ optimization library.

  *

  * Copyright (C) 2003-2008

  * Egervary Jeno Kombinatorikus Optimalizalasi Kutatocsoport

  * (Egervary Research Group on Combinatorial Optimization, EGRES).

  *

  * Permission to use, modify and distribute this software is granted

  * provided that this copyright notice appears in all copies. For

  * precise terms see the accompanying LICENSE file.

  *

  * This software is provided "AS IS" with no warranty of any kind,

  * express or implied, and with no claim as to its suitability for any

  * purpose.

  *

  */

 namespace lemon {

 /*!

 \page lgf-format Lemon Graph Format (LGF)

 The \e LGF is a <em>column oriented</em>

 file format for storing graphs and associated data like

 node and edge maps.

 Each line with \c '#' first non-whitespace

 character is considered as a comment line.

 Otherwise the file consists of sections starting with

 a header line. The header lines starts with an \c '@' character followed by the

 type of section. The standard section types are \c \@nodes, \c

 \@arcs and \c \@edges

 and \@attributes. Each header line may also have an optional

 \e name, which can be use to distinguish the sections of the same

 type.

 The standard sections are column oriented, each line consists of

 <em>token</em>s separated by whitespaces. A token can be \e plain or

 \e quoted. A plain token is just a sequence of non-whitespace characters,

 while a quoted token is a

 character sequence surrounded by double quotes, and it can also

 contain whitespaces and escape sequences.

 The \c \@nodes section describes a set of nodes and associated

 maps. The first is a header line, its columns are the names of the

 maps appearing in the following lines.

 One of the maps must be called \c

 "label", which plays special role in the file.

 The following

 non-empty lines until the next section describes nodes of the

 graph. Each line contains the values of the node maps

 associated to the current node.

 \code

  @nodes

  label  coordinates  size    title

  1      (10,20)      10      "First node"

  2      (80,80)      8       "Second node"

  3      (40,10)      10      "Third node"

 \endcode

 The \c \@arcs section is very similar to the \c \@nodes section,

 it again starts with a header line describing the names of the maps,

 but the \c "label" map is not obligatory here. The following lines

 describe the arcs. The first two tokens of each line are

 the source and the target node of the arc, respectively, then come the map

 values. The source and target tokens must be node labels.

 \code

  @arcs

          capacity

  1   2   16

  1   3   12

  2   3   18

 \endcode

 The \c \@edges is just a synonym of \c \@arcs. The @arcs section can

 also store the edge set of an undirected graph. In such case there is

 a conventional method for store arc maps in the file, if two columns

 has the same caption with \c '+' and \c '-' prefix, then these columns

 can be regarded as the values of an arc map.

 The \c \@attributes section contains key-value pairs, each line

 consists of two tokens, an attribute name, and then an attribute

 value. The value of the attribute could be also a label value of a

 node or an edge, or even an edge label prefixed with \c '+' or \c '-',

 which regards to the forward or backward directed arc of the

 corresponding edge.

 \code

  @attributes

  source 1

  target 3

  caption "LEMON test digraph"

 \endcode

 The \e LGF can contain extra sections, but there is no restriction on

 the format of such sections.

 */

 }

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