When plotting arrays of curves, plot lines only in the direction

of (in absolute terms) growing x values.
Example: MOS output characteristics.
In the rare case of plotting versus varying x directions
(e.g. example memristor.sp), one has to add the flag
'retraceplot' to the plot command.

examples/memristor/memristor.sp

@@ -57,9 +57,9 @@ plot tran1.alli tran2.alli alli title 'Memristor with threshold: Internal Progra
 settype impedance xmem.x1 tran1.xmem.x1 tran2.xmem.x1
 plot xmem.x1 tran1.xmem.x1 tran2.xmem.x1 title 'Memristor with threshold: resistance'
 * resistance versus voltage (change occurs only above threshold!)
-plot xmem.x1 vs v(1) tran1.xmem.x1 vs tran1.v(1) tran2.xmem.x1 vs tran2.v(1) title 'Memristor with threshold: resistance'
+plot xmem.x1 vs v(1) tran1.xmem.x1 vs tran1.v(1) tran2.xmem.x1 vs tran2.v(1) retraceplot title 'Memristor with threshold: resistance'
 * current through resistor for all plots versus voltage
-plot i(v1) vs v(1) tran1.i(v1) vs tran1.v(1) tran2.i(v1) vs tran2.v(1) title 'Memristor with threshold: external current loops'
+plot i(v1) vs v(1) tran1.i(v1) vs tran1.v(1) tran2.i(v1) vs tran2.v(1) retraceplot title 'Memristor with threshold: external current loops'
 .endc
 
 .end

examples/memristor/memristor_x.sp

@@ -47,11 +47,11 @@ Rmem plus minus r={V(x)}
 op 
 print all
 ac lin 101 1 100k
-plot v(11)
+*plot v(11)
 * approx. 100 simulation points
 let deltime = stime/100
 tran $&deltime $&stime uic
-* plot i(v1) vs v(1)
+*plot i(v1) vs v(1) retrace
 *** you may just stop here ***
 * raise the frequency
 let newfreq = 1.2/stime
@@ -75,9 +75,9 @@ let res2 = tran2.v(1)/(tran2.I(v1) + 1e-16)
 settype impedance res res1 res2
 plot res vs time res1 vs tran1.time res2 vs tran2.time  title 'Memristor with threshold: resistance'
 * resistance versus voltage (change occurs only above threshold!)
-plot res vs v(1) res1 vs tran1.v(1) res2 vs tran2.v(1) title 'Memristor with threshold: resistance'
+plot res vs v(1) res1 vs tran1.v(1) res2 vs tran2.v(1) retraceplot title 'Memristor with threshold: resistance'
 * current through resistor for all plots versus voltage
-plot i(v1) vs v(1) tran1.i(v1) vs tran1.v(1) tran2.i(v1) vs tran2.v(1) title 'Memristor with threshold: external current loops'
+plot i(v1) vs v(1) tran1.i(v1) vs tran1.v(1) tran2.i(v1) vs tran2.v(1) retraceplot title 'Memristor with threshold: external current loops'
 .endc
 
 .end

src/frontend/plotting/gnuplot.c

@@ -319,7 +319,7 @@ void ft_gnuplot(double *xlims, double *ylims,
     (void) fclose(file);
 
     /* Write out the data and setup arrays */
-    bool mono = (plottype == PLOT_MONOLIN);
+    bool mono = (plottype != PLOT_RETLIN);
     dir = 0;
     prev_xval = NAN;
     for (i = 0; i < scale->v_length; i++) {

src/frontend/plotting/plotcurv.c

@@ -130,7 +130,7 @@ ft_graf(struct dvec *v, struct dvec *xs, bool nostart)
      * interpolation.
      */
     if ((degree == 1) && (gridsize == 0)) {
-        bool mono = (currentgraph->plottype == PLOT_MONOLIN);
+        bool mono = (currentgraph->plottype != PLOT_RETLIN);
         dir = 0;
         for (i = 0, j = v->v_length; i < j; i++) {
             dx = isreal(xs) ? xs->v_realdata[i] :

src/frontend/plotting/plotit.c

@@ -600,14 +600,14 @@ bool plotit(wordlist *wl, const char *hcopy, const char *devname)
             pfound = TRUE;
         }
     }
-    if (getflag(wl, "noretraceplot")) {
+    if (getflag(wl, "retraceplot")) {
         if (pfound) {
             fprintf(cp_err,
                     "Warning: too many plot types given. "
-                    "\"noretraceplot\" is ignored.\n");
+                    "\"retraceplot\" is ignored.\n");
         }
         else {
-            ptype = PLOT_MONOLIN;
+            ptype = PLOT_RETLIN;
             pfound = TRUE;
         }
     }
@@ -640,8 +640,8 @@ bool plotit(wordlist *wl, const char *hcopy, const char *devname)
             if (eq(buf, "linplot")) {
                 ptype = PLOT_LIN;
             }
-            else if (eq(buf, "noretraceplot")) {
-                ptype = PLOT_MONOLIN;
+            else if (eq(buf, "retraceplot")) {
+                ptype = PLOT_RETLIN;
             }
             else if (eq(buf, "combplot")) {
                 ptype = PLOT_COMB;

src/include/ngspice/dvec.h

@@ -22,7 +22,7 @@ enum dvec_flags {
 
 /* Plot types. */
 typedef enum {
-    PLOT_LIN, PLOT_COMB, PLOT_POINT, PLOT_MONOLIN
+    PLOT_LIN, PLOT_COMB, PLOT_POINT, PLOT_RETLIN
 } PLOTTYPE;