pl_fspace_r (chart->lp, 0.0, 0.0, 1000.0, 1000.0); /* set coordinate system */
pl_flinewidth_r (chart->lp, 0.25); /* set line thickness */
pl_pencolorname_r (chart->lp, "black");
pl_fspace_r (chart->lp, 0.0, 0.0, 1000.0, 1000.0); /* set coordinate system */
pl_flinewidth_r (chart->lp, 0.25); /* set line thickness */
pl_pencolorname_r (chart->lp, "black");