=head1 NAME
Math::LP::Solve - perl wrapper for the lp_solve linear program solver
=head1 SYNOPSIS
use Math::LP::Solve qw(:ALL); # imports all functions and variables
# construct an LP with 0 initial constraints and 2 variables
$lp = make_lp(0,2);
# add the constraint x1 + 2 x2 <= 3
$coeffs = ptrcreate('double',0.0,2); # mallocs a C array
ptrset($coeffs,1.0,0);
ptrset($coeffs,2.0,1);
add_constraint($lp,$coeffs,$LE,3);
ptrfree($coeffs); # frees the C array
# set the objective function to x1+x2 and solve for a maximum
$obj = ptrcreate('double',1.0,2);
set_obj_fn($lp,$obj);
ptrfree($obj);
set_maxim($lp);
# solve the LP
solve($lp) == $OPTIMAL or die "No solution found";
$solution = lprec_best_solution_get($lp);
# extract the results from the solution array
$obj_fn_val = ptrvalue($solution,0);
$constr_val = ptrvalue($solution,1);
$x1 = ptrvalue($solution,2);
$x2 = ptrvalue($solution,3);
=head1 DESCRIPTION
Math::LP::Solve is a wrapper around the freeware lp_solve library,
which solves linear and mixed linear/integer programs. Most functions
and data structures in the file lpkit.h of the lp_solve distribution
are made available in the Math::LP::Solve namespace.
This document does not go into the details of how to setup and
solve a linear program using the lp_solve library. For details
on this you are referred to the documentation included in the source
code for lp_solve.
That being said, a few details of the Perl wrappers around the underlying
lp_solve library need explaining in order to be able to use them.
(For those interested, the wrapping was done using SWIG, more info
at http://www.swig.org/)
All symbols (functions and variables) are divided into 4 categories.
All these symbols are in the C namespace and are not
exported by default. They are however tagged so that you can easily
import them into your own code. The following C<%EXPORT_TAGS> are available:
=over 4
=item ptrlib
pointer library functions, needed to handle C-style arrays;
=item accessors
pairs of get/set functions to access data fields of structs;
=item functions
wrappers for lp_solve library functions;
=item scalars
perl scalar variables mapping C<#define>'d constants in lpkit.h.
=back
A 5th category named B is available in C<%EXPORT_TAGS>, which includes all
symbols of the 4 mentioned categories.
=head2 Pointer library functions
The pointer library functions are needed to pass arrays of coefficients etc.
to and from the lp_solve functions and data structures. In the underlying
C library, this is done using C pointers, which are not available
in Perl. The pointer library functions provide a Perl interface to get
around this problem.
There are several pointer library functions, and they are fully explained
in the SWIG documentation. However, the following is all you need to
know to use them with lp_solve:
=over 4
=item ptrcreate($type,$initval,$size)
Creates and returns a pointer to type C<$type>, which is an array with C<$size>
fields initialized to C<$initval>. E.g. an array of 2 doubles initialized
to zero is created with the command
$arr_double = Math::LP::Solve::ptrcreate('double',0.0,2);
=item ptrset($ptr,$val,$index)
sets the value of the C<$index>'th field of the array pointed to in C<$ptr>
to the value C<$val>. E.g. the 2nd entry of an array of doubles is set to 3.14
using
Math::LP::Solve::ptrset($arr_double,3.14,1);
Note that the 1st entry is denoted by index 0, as in C.
=item ptrvalue($ptr,$index)
returns the C<$index>'th entry of the array pointed to in C<$ptr>.
E.g. the 1st value of an array of doubles is requested using
$d0 = Math::LP::Solve::ptrvalue($arr_double,0);
=item ptrfree($ptr)
frees the memory allocated for C<$ptr>. Always do this when you are finished
with an array you allocated yourself using ptrcreate(), or you will end up
with memory leaks. Also, take care not to invoke ptrfree() twice on the same
pointer if it is not re-created.
=back
=head2 Functions
The functions have the same name as in C. Note however that C
parameters need to be handled with the aforementioned pointer library
functions. The pointer library functions are not needed for the C
parameters, as their creation, manipulation and freeing is completely
covered by the C functions. E.g. an LP is created with
$lp = Math::LP::Solve::make_lp(0,0);
subsequently manipulated with
Math::LP::Solve::set_obj_fn($lp,$arr_double);
and finally freed using
Math::LP::Solve::delete_lp($lp);
Some functions have been added to the ones available in C
to ease file manipulation and handling names of rows and columns:
=over 4
=item lprec_lp_name_get($lp)
returns the name of the LP;
=item lprec_lp_name_set($lp,$name)
sets the name of the LP to C<$name>;
=item lprec_row_name_get($lp,$i) and lprec_col_name_get($lp,$i)
returns the name of the row resp. column with index C<$i>;
=item lprec_row_name_set($lp,$i,$name) and lprec_col_name_set($lp,$i,$name)
sets the name of the row resp. column with index C<$i> to C<$name>;
=item open_file($filename,$mode)
opens the file C<$filename> with mode C<$mode>, which is specified as a
string. Calls the C function fopen() internally;
=item close_file($fh)
closes a filehandle obtained with open_file().
=back
=head2 Constants
Following constants are available in the Math::LP::Solve namespace:
=over 4
=item General constants
C<$DEF_INFINITE>
=item Constraint types
C<$LE>, C<$EQ>, C<$GE> and C<$OF>
=item Boolean values
C<$TRUE> and C<$FALSE>
=item Status values obtained from solve()
C<$OPTIMAL>, C<$MILP_FAIL>, C<$INFEASIBLE>, C<$UNBOUNDED>, C<$FAILURE>
and C<$RUNNING>
=item Extra status values obtained from lag_solve()
C<$FEAS_FOUND>, C<$NO_FEAS_FOUND> and C<$BREAK_BB>
=back
=head2 Data field accessors
Each data field in C can be queried from a Perl variable
holding an LP using C and
set using C.
Note that the row and column names are accessed using the functions
lprec_row_name_get(), lprec_col_name_get(), lprec_row_name_set() and
lprec_col_name_set() described above.
=head1 SEE ALSO
=over 4
=item
The underlying lp_solve library has been written by Michel Berkelaar
and adapted by Jeroen Dirks.
Its source code is available at ftp://ftp.ics.ele.tue.nl/pub/lp_solve/
=item
More information on the exporting of symbols is found in L.
=item
The wrapping of the C library was done with the aid of SWIG.
The SWIG homepage is located at http://www.swig.org/
=item
An object oriented interface to the lp_solve library has been written
on top of Math::LP::Solve. For more info look at L.
=back
=head1 AUTHOR
Wim Verhaegen Ewimv@cpan.orgE
=head1 COPYRIGHT
Copyright (c) 2000-2001 Wim Verhaegen. All rights reserved.
This program is free software; you can redistribute
and/or modify it under the same terms as Perl itself.
Consult the lp_solve documentation for copyright information on
the lp_solve library.
=cut