COIN-OR::LEMON - Graph Library

Changeset 1514:c9b9bc63db4e in lemon-0.x for doc/quicktour.dox


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Timestamp:
06/24/05 23:03:08 (14 years ago)
Author:
athos
Branch:
default
Phase:
public
Convert:
svn:c9d7d8f5-90d6-0310-b91f-818b3a526b0e/lemon/trunk@1998
Message:

Improved getsart.dox and quicktour.dox

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1 edited

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  • doc/quicktour.dox

    r1511 r1514  
    1919about \ref graphs "graphs".
    2020
    21 You will also want to assign data to the edges or nodes of the graph, for example a length or capacity function defined on the edges. You can do this in LEMON using so called \ref maps "maps". You can define a map on the nodes or on the edges of the graph and the value of the map (the range of the function) can be practically almost of any type. Read more about maps \ref maps-page "here".
     21You will also want to assign data to the edges or nodes of the graph, for
     22example a length or capacity function defined on the edges. You can do this in
     23LEMON using so called \b maps. You can define a map on the nodes or on the edges of the graph and the value of the map (the range of the function) can be practically almost of any type. Read more about maps \ref maps-page "here".
    2224
    2325Some examples are the following (you will find links next to the code fragments that help to download full demo programs: save them on your computer and compile them according to the description in the page about \ref getsart How to start using LEMON):
    2426
    25 - First we give two examples that show how to instantiate a graph. The
     27<ul>
     28<li> First we give two examples that show how to instantiate a graph. The
    2629first one shows the methods that add nodes and edges, but one will
    2730usually use the second way which reads a graph from a stream (file).
    28 -# The following code fragment shows how to fill a graph with data. It creates a complete graph on 4 nodes. The type Listgraph is one of the LEMON graph types: the typedefs in the beginning are for convenience and we will suppose them later as well.
     31<ol>
     32<li>The following code fragment shows how to fill a graph with data. It creates a complete graph on 4 nodes. The type Listgraph is one of the LEMON graph types: the typedefs in the beginning are for convenience and we will suppose them later as well.
    2933 \code
    3034  typedef ListGraph Graph;
     
    4347See the whole program in file \ref helloworld.cc.
    4448
    45 If you want to read more on the LEMON graph structures and concepts, read the page about \ref graphs "graphs".
    46 
    47 -# The following code shows how to read a graph from a stream (e.g. a file). LEMON supports the DIMACS file format: it can read a graph instance from a file
     49    If you want to read more on the LEMON graph structures and concepts, read the page about \ref graphs "graphs".
     50
     51<li> The following code shows how to read a graph from a stream (e.g. a file). LEMON supports the DIMACS file format: it can read a graph instance from a file
    4852in that format (find the documentation of the DIMACS file format on the web).
    4953\code
     
    5458One can also store network (graph+capacity on the edges) instances and other things in DIMACS format and use these in LEMON: to see the details read the documentation of the \ref dimacs.h "Dimacs file format reader".
    5559
    56 
    57 - If you want to solve some transportation problems in a network then
     60</ol>
     61<li> If you want to solve some transportation problems in a network then
    5862you will want to find shortest paths between nodes of a graph. This is
    5963usually solved using Dijkstra's algorithm. A utility
     
    130134
    131135
    132 - If you want to design a network and want to minimize the total length
     136<li> If you want to design a network and want to minimize the total length
    133137of wires then you might be looking for a <b>minimum spanning tree</b> in
    134138an undirected graph. This can be found using the Kruskal algorithm: the
     
    138142Ide Zsuzska fog irni!
    139143
    140 -
     144<li>Many problems in network optimization can be formalized by means of a
     145linear programming problem (LP problem, for short). In our library we decided
     146not to write an LP solver, since such packages are available in the commercial
     147world just as well as in the open source world, and it is also a difficult
     148task to compete these. Instead we decided to develop an interface that makes
     149it easier to use these solvers together with LEMON. So far we have an
     150interface for the commercial LP solver software \b CLPLEX (developed by ILOG)
     151and for the open source solver \b GLPK (a shorthand for Gnu Linear Programming
     152Toolkit).
     153
     154We will show two examples, the first one shows how simple it is to formalize
     155and solve an LP problem in LEMON, while the second one shows how LEMON
     156facilitates solving network optimization problems using LP solvers.
     157
     158<ol>
     159<li>The following code shows how to solve an LP problem using the LEMON lp
     160interface.
    141161
    142162\code
    143163
     164  //A default solver is taken
     165  LpDefault lp;
     166  typedef LpDefault::Row Row;
     167  typedef LpDefault::Col Col;
     168 
     169
     170  //This will be a maximization
     171  lp.max();
     172
     173  //We add coloumns (variables) to our problem
     174  Col x1 = lp.addCol();
     175  Col x2 = lp.addCol();
     176  Col x3 = lp.addCol();
     177
     178  //Constraints
     179  lp.addRow(x1+x2+x3 <=100); 
     180  lp.addRow(10*x1+4*x2+5*x3<=600); 
     181  lp.addRow(2*x1+2*x2+6*x3<=300); 
     182  //Nonnegativity of the variables
     183  lp.colLowerBound(x1, 0);
     184  lp.colLowerBound(x2, 0);
     185  lp.colLowerBound(x3, 0);
     186  //Objective function
     187  lp.setObj(10*x1+6*x2+4*x3);
     188 
     189  //Call the routine of the underlying LP solver
     190  lp.solve();
     191
     192  //Print results
     193  if (lp.primalStatus()==LpSolverBase::OPTIMAL){
     194    printf("Z = %g; x1 = %g; x2 = %g; x3 = %g\n",
     195           lp.primalValue(),
     196           lp.primal(x1), lp.primal(x2), lp.primal(x3));
     197  }
     198  else{
     199    std::cout<<"Optimal solution not found!"<<std::endl;
     200  }
     201
     202
    144203\endcode
    145204
     205See the whole code in \ref lp_demo.cc.
     206
     207<li>The second example shows how easy it is to formalize a network
     208optimization problem as an LP problem using the LEMON LP interface.
     209
     210</ol>
     211</ul>
    146212
    147213*/
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