avoid retrace in output graph by adding label 'noretraceplot'

to the plot command, that creates a lin plot trying to avoid retracing

src/frontend/plotting/graf.c

@@ -267,7 +267,7 @@ gr_point(struct dvec *dv,
     switch (currentgraph->plottype) {
         double    *tics;
     case PLOT_LIN:
-
+    case PLOT_MONOLIN:
         /* If it's a linear plot, ignore first point since we don't
            want to connect with oldx and oldy. */
         if (np)

src/frontend/plotting/plotcurv.c

@@ -130,6 +130,7 @@ ft_graf(struct dvec *v, struct dvec *xs, bool nostart)
      * interpolation.
      */
     if ((degree == 1) && (gridsize == 0)) {
+        bool mono = (currentgraph->plottype == PLOT_MONOLIN);
         dir = 0;
         for (i = 0, j = v->v_length; i < j; i++) {
             dx = isreal(xs) ? xs->v_realdata[i] :
@@ -137,7 +138,7 @@ ft_graf(struct dvec *v, struct dvec *xs, bool nostart)
             dy = isreal(v) ? v->v_realdata[i] :
                 realpart(v->v_compdata[i]);
             if ((i == 0 || (dir > 0 ? lx > dx : dir < 0 ? lx < dx : 0)) &&
-                xs->v_plot && xs->v_plot->pl_scale == xs)
+                (mono || (xs->v_plot && xs->v_plot->pl_scale == xs)))
             {
                 gr_point(v, dx, dy, lx, ly, 0);
             } else {

src/frontend/plotting/plotit.c

@@ -454,6 +454,14 @@ plotit(wordlist *wl, char *hcopy, char *devname)
             pfound = TRUE;
         }
     }
+    if (getflag(wl, "noretraceplot")) {
+        if (pfound) {
+            fprintf(cp_err, "Warning: too many plot types given\n");
+        } else {
+            ptype = PLOT_MONOLIN;
+            pfound = TRUE;
+        }
+    }
     if (getflag(wl, "combplot")) {
         if (pfound) {
             fprintf(cp_err, "Warning: too many plot types given\n");
@@ -475,6 +483,8 @@ plotit(wordlist *wl, char *hcopy, char *devname)
         if (cp_getvar("plotstyle", CP_STRING, buf)) {
             if (eq(buf, "linplot"))
                 ptype = PLOT_LIN;
+            else if (eq(buf, "noretraceplot"))
+                ptype = PLOT_MONOLIN;
             else if (eq(buf, "combplot"))
                 ptype = PLOT_COMB;
             else if (eq(buf, "pointplot"))

src/include/ngspice/dvec.h

@@ -20,7 +20,7 @@ enum dvec_flags {
 
 /* Plot types. */
 typedef enum {
-    PLOT_LIN, PLOT_COMB, PLOT_POINT
+    PLOT_LIN, PLOT_COMB, PLOT_POINT, PLOT_MONOLIN
 } PLOTTYPE;