Improving graph quality

Ran a code with portion below. However, the quality of graphs is of poor quality for some reasons.

Please any help on how to fix the issue?
Thanks
Ozey

library optmum,pgraph;
graphset;
#include optmum.ext;
_opalgr=2;_opmiter=300;__output=2;_oprteps=0;
_pcolor=4|1|4|2;_pltype=6|6|6|1;_opgtol=1e-3;
_pmcolor=0|0|1|1|1|0|0|0|15;
pqgwin many;

You don't want to use the pgraph library. It is old and kept around only for backward compatibility. Take a look at these GAUSS graphics blogs to see how to make better graphs.

Feel free to post a new question on the forum if you need help with your graph.