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GAMS supports the option of outputting numerous run statistics to a data text file known as the trace file. The use of the trace file is useful, for example, if batch runs are done using several solvers on a model test set and performance statistics are to be obtained; GAMS appends to the tracefile, if it already exists.

Using the GAMS trace option

The trace option is invoked by using the command trace=(filename). If we were to run the model trnsport.gms from the GAMS Model Library from the command line we would specify:
     >> gams trnsport trace=(filename) traceopt=(integer)
where (filename) is the name of the trace file to be created.

The trace feature supports several options, that is several different types of trace files can be created, depending on what output information is desired. The different trace file options are obtained by specifying traceopt=(integer), where (integer) can take a value of 1-3. For our tools in the Performance World we will make use of traceopt=3 unless otherwise noted. Using this option from the GAMS IDE, we would specify:
        trace=(filename) traceopt=3
in the GAMS parameter list box. A sample trace file is trace1.trc where the file includes statistics of GAMS runs over all LP models in LINLib for a single solver A. We list the solver used as "A" in order to hide proprietary data of the real solver used.


The tracefile option appends to any previous trace file. That is, if a previous trace file of the same name already exists, then all new data output will be appended. Users should be careful to make sure that all old versions of the trace file are deleted if the same filename is used.

Trace file parameters

The column headers for traceopt=3 are as follows:

        1. filename:    GAMS model filename           
        2. modeltype:   LP, MIP, NLP, etc.	       
        3. solvername:  			       
        4. NLP def:     default NLP solver 	       
        5. MIP def:     default MIP solver	       
        6. juliantoday: start day/time of job	       
        7. direction:   0=min, 1=max		       
        8. equnum:      total number of equations     
        9. varnum:	 total number of variables     
       10. dvarnum:     number of discrete variables  
       11. nz:          number of nonzeros	       
       12. nlnz:        number of nonlinear nonzeros  
       13. optfile:     1= optfile included	       
       14. modelstatus: GAMS model return status - see the GAMS return codes section.         
       15. solvestatus:	GAMS solver return status - see the GAMS return codes section.    
       16. obj:         value of objecive function    
       17. objest:      objective function estimate   
       18. res used:    resource time used (sec)      
       19. iter used:   number of solver iterations   
       20. dom used:    			       
       21. nodes used:				       
       22. user1:       user comment - preceded by a #	

The final column (22. user1:) is obtained by specifying u1=(comment) on the command line or the GAMS IDE parameter list box. This will append the text # comment to the end of each line.