GAMS: GDXDUMP and Equations

There is a fairly deep issue when comparing GDX files if one of the GDX files has the following properties:

1. It is produced by GDXDUMP
2. It contains Equation records

The following illustrates the problem:

C:\projects\tmp>gamslib indus89 Copy ASCII: indus89.gms C:\projects\tmp>gams indus89 lo=0 gdx=1 C:\projects\tmp>gdxdump 1.gdx output=2.gms *  GDX dump of 1.gdx *  Library in use : C:\PROGRA~1\GAMS23.7 *  Library version: GDX Library      BETA  8Jun11 23.7.0 WEX 25828.25830 WEI x86_64/MS Windows *  File version   : GDX Library      BETA  8Jun11 23.7.0 WEX 25828.25830 WEI x86_64/MS Windows *  Producer       : GAMS Base Module BETA  8Jun11 23.7.0 WEX 25828.25830 WEI x86_64/MS Windows *  File format    :    7 *  Compression    :    0 *  Symbols        :  281 *  Unique Elements:  245 C:\projects\tmp>gams 2.gms lo=0 gdx=2 C:\projects\tmp>gdxdiff 1.gdx 2.gdx eps=1.0e-6 GDXDIFF          BETA  8Jun11 23.7.0 WEX 25828.25830 WEI x86_64/MS Windows File1 : 1.gdx File2 : 2.gdx Summary of differences:    bdraft   Data are different    brepco   Data are different   ccombal   Data are different   consbal   Data are different      cost   Data are different    demnat   Data are different divcnlsea   Data are different    divsea   Data are different    fodder   Data are different    grnfdr   Data are different    laborc   Data are different      nbal   Data are different   nwfpalc   Data are different      objn   Data are different     objnn   Data are different      objz   Data are different     objzn   Data are different   protein   Data are different    prseaw   Data are different   qcombal   Data are different   subirrc   Data are different    tdraft   Data are different watalcpro   Data are different watalcsea   Data are different   watalcz   Data are different waterbaln   Data are different Output: diffile.gdx GDXDiff finished C:\projects\tmp>gdxdump diffile.gdx Symbols *  GDX dump of diffile.gdx *  Library in use : C:\PROGRA~1\GAMS23.7 *  Library version: GDX Library      BETA  8Jun11 23.7.0 WEX 25828.25830 WEI x86_64/MS Windows *  File version   : GDX Library      BETA  8Jun11 23.7.0 WEX 25828.25830 WEI x86_64/MS Windows *  Producer       : GDXDIFF *  File format    :    7 *  Compression    :    0 *  Symbols        :   26 *  Unique Elements:  249    Symbol    Dim Type  Explanatory text 1 bdraft      4  Equ  Differences 2 brepco      3  Equ  Differences 3 ccombal     4  Equ  Differences 4 consbal     4  Equ  Differences 5 cost        3  Equ  Differences 6 demnat      3  Equ  Differences 7 divcnlsea   3  Equ  Differences 8 divsea      2  Equ  Differences 9 fodder      4  Equ  Differences 10 grnfdr      4  Equ  Differences 11 laborc      4  Equ  Differences 12 nbal        3  Equ  Differences 13 nwfpalc     2  Equ  Differences 14 objn        1  Equ  Differences 15 objnn       1  Equ  Differences 16 objz        1  Equ  Differences 17 objzn       1  Equ  Differences 18 protein     4  Equ  Differences 19 prseaw      3  Equ  Differences 20 qcombal     4  Equ  Differences 21 subirrc     4  Equ  Differences 22 tdraft      4  Equ  Differences 23 watalcpro   3  Equ  Differences 24 watalcsea   3  Equ  Differences 25 watalcz     4  Equ  Differences 26 waterbaln   4  Equ  Differences C:\projects\tmp>

Apart from a small bug related to $ONEMPTY, it turns out that the way GDXDUMP exports equations records, it looses information about the equation type. This leads to the above results. Luckily in practice this will not be an issue, as equations are not often part of such an exercise.

Background.

During a course I taught about GAMS I was asked if it is possible to edit GDX files. The answer is: GDXDUMP will give you a GAMS representation of a GDX file which you can edit. Using the call:

GAMS gmsfile gdx=newgdxfile

you can make a new GDX file with the changes incorporated. The tool GDXDIFF will allow you to monitor the changes.

Although this is correct, I chose the INDUS89 example as illustration. That was unfortunate, as that failed because of the exotic Equation problem.