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

 *

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

 *

 * Copyright (C) 2003-2009

 * 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 \e LGF files can also contain bipartite graphs, in this case a

\c @red_nodes and a \c @blue_nodes sections describe the node set of the

graph. If a map is in both of these sections, then it can be used as a

regular node map.

\code

 @red_nodes

 label  only_red_map   name

 1      "cherry"       "John"

 2      "Santa Claus"  "Jack"

 3      "blood"        "Jason"

 @blue_nodes

 label  name

 4      "Elisabeth"

 5      "Eve"

\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

If there is no map in the \c \@arcs section at all, then it must be

indicated by a sole '-' sign in the first line.

\code

 @arcs

         -

 1   2

 1   3

 2   3

\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

have 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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