The intent of psgsimp is to remove excessive detail from an automatically-generated input file before plotting it with psgraph. This can significantly reduce the amount of time it takes to print the resulting PostScript file, without much affecting the final output.
The meaning of threshold-pct is that psgsimp should suppress any point which differs from its predecessor by less than this value in both the X and Y directions. For example, if threshold-pct is 1.0, then any change of less than one per cent is suppressed. Lables, markers, and the end points of lines are always plotted; only the intermediate points are ever suppressed.
The time reduction can be quite dramatic; for example, one graph that contains 37,000 points took over 16 minutes to plot on an LPS-20. Using a simplification threshold of 1.0, which eliminates details too small to be seen on the final plot, psgsimp reduced the size of the input file to about 6,000 points. The resulting PostScript file took about two minutes to print, and was indistinguishable from the unsimplified version.
Note that you may have to experiment somewhat with different values for threshold-pct, since some graphs will suffer more from simplification than others.
The output file contains all the removed input points as comments; this allows you to add back any points you want if you think the result will look better. To remove these comments (and perhaps reclaim some disk space) use ``grep -v "##"''.