USAGE: change_cost [options] groebner_file new_cost_file
            
             
           
DESCRIPTION:
             
change_cost is a program for recomputing the reduced Groebner basis of
a toric ideal with respect to a term ordering with modified
weights. This can be used for varying the cost function in integer
programming (see the help for solve_IP for more information).
The program simply restarts Buchberger´s algorithm on an already
computed toric ideal using the modified term ordering.               
            
                
      
FILE FORMAT:
               
The first input file has to be a GROEBNER file; the second input file
should to be a NEW_COST file. For convenience, also MATRIX files are
accepted as second input files. For their format see the help for the
solve_IP or the toric_ideal program.  
               
change_cost writes the new Groebner basis into a GROEBNER file named
like the second input file with extensions replaced by
          
	.GB.<alg>
              
where GB stands for GROEBNER and <alg> is the abbreviation of the
algorithm used for computing the input GROEBNER file (see the help for 
solve_IP or toric_ideal for an explaination).
               
A GROEBNER file looks as follows:
         
         
  GROEBNER 
            
  computed with algorithm:
  <algorithm name abbreviation>       (* abbreviations as above *)
  from file(s):                       (* the following four lines are 
  <name of respective MATRIX file>       optional *)
  computation time:                     
  <computation time in seconds>          
             
  term ordering:
  elimination block
  <number of elimination variables>
  <LEX / DEG_LEX                      (* only if number of elimination
  / DEG_REV_LEX>                         variables >0 *)
  weighted block
  <number of weighted variables>
  <W_LEX / W_REV_LEX                  (* number of weighted variables    
  / W_DEG_LEX / W_DEG_REV_LEX>           should always be >0 *)
  <weight_vector>
             
  size:
  <number of elements>
          
  Groebner basis:
  <basis elements>                   
            
  <settings for the Buchberger 
   algorithm and compiler settings>  (* optional *)		
            
                  
The Groebner basis consists always of binomials of the form x^a - x^b
where x^a and x^b are relatively prime. Such a binomial can be
represented by the vector a-b. The basis elements in the GROEBNER file 
are given by the coefficients of this vector representation.
The settings for Buchberger´s algorithm and the compiler flags are
produced when the GROEBNER file is generated by a call of solve_IP
with the verbose output option
          
	-v, --verbose  
             
Example:
         
         
  GROEBNER
         
  computed with algorithm:
  du
        
  term ordering:	
  elimination block:
  0
  weighted block:
  3
  W_LEX
  1 2 3
           
  size:
  1
              
  Groebner basis:
  2 3 -2			    (*  x^2 * y^3 - z^2  *) 
           
               
A NEW_COST file should look as follows:
           
            
  NEW_COST              
            
  variables:			
  <number of weighted variables>         
              
  cost vector:
  <coefficients of the new weight vector>       
               
        
                
OPTIONS: 
          
 -p         <number>      percentage of new generators to cause an
                          autoreduction during Buchberger´s algorithm; 
                          <number> may be an arbitrary float, a
                          negative value allows no intermediate
                          autoreductions
			  default is 
                          -p 12.0  
                
 -S [RP] [M] [B] [M] [2]  criteria to use in Buchberger´s algorithm
                          for discarding unneccessary S-pairs
             RP           relatively prime leading terms
             M            Gebauer-Moeller criterion M
             F            Gebauer-Moeller criterion F
             B            Gebauer-Moeller criterion B
             2            Buchberger´s second criterion
			  default is 
                          -S RP M B 		
             
 -v,          
--verbose                 verbose output mode; writes the settings for 
                          Buchberger´s algorithm and the compiler
                          flags into the output GROEBNER file 
             
-V <number>, 
--version <number>        version of Buchberger´s algorithm to use;
                          <number> may be 1, 1a, 2 or 3
			  default is
                          -V 1	
                  
