Writing older GDX versions with GDXCONVERT

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Over time GDX file formats have changed. Some environments have multiple GAMS versions some of which are older and file format compatibility can become an issue. Consequently one may need to write GDX files in an older GDX file format. This may be done using the environment variable or GAMS parameter gdxconvert and possibly gdxcompress.

Gdx file formats are named v5, v6 or v7 and can be compressed or not compressed.

•	v5 applies to GDX files written by GAMS versions 22.2 and earlier.

•	v6 were introduced with version 22.3 of GAMS and lasted through 22.5.

•	v7 formatted files were introduced with version 22.6 of GAMS.

•	GAMS platforms that were introduced after 22.3/22.6 (e.g. Mac Intel or SunSparc64) do not support V5/V6.

•	gdxcompress allows one to tun on and off compression.

There are two ways of implementing this through environment variables and through a GAMS command line parameter. Command line options have higher precedence than the environment variables with the same name.