Add variable 'plainplot' to allow plotting without

function support, but with node names incl chatacters like + - /.
Flag to command 'plot' is renamed to plainplot.
Error message added if vector not found.
Example file added.

examples/various/nmos_out_BSIM330_plainwrite.sp

@@ -0,0 +1,46 @@
+*****  NMOS Transistor BSIM3 (Id-Vds) with Rd ***
+** Node name with offensive character '+'
+
+M1 2 1 3 4 n1 W=1u L=0.35u Pd=1.5u Ps=1.5u ad=1.5p as=1.5p
+vgs 1 0 3.5 
+vds 2 0 0.1 
+vss 3 0 0
+vbs 4 0 0
+
+* drain series resistor
+R2 2 22 1k
+M2 22 1 +32 4 n1 W=1u L=0.35u Pd=1.5u Ps=1.5u ad=1.5p as=1.5p
+vss2 +32 0 0
+
+
+.options Temp=27.0
+
+* BSIM3v3.3.0 model with modified default parameters 0.18µm
+.model n1 nmos level=49 version=3.3.0 tox=3.5n nch=2.4e17 nsub=5e16 vth0=0.15
+.model p1 pmos level=49 version=3.3.0 tox=3.5n nch=2.5e17 nsub=5e16 vth0=-0.15
+
+.control
+set xgridwidth=2
+set xbrushwidth=3
+dc vds 0 2 0.05 vgs 0 2 0.4
+let v(/22) = V(22) ; only availavle in plot dc1
+dc vds 0 2 0.05 vgs 0 2 0.5
+
+let v(+22) = V(22) ; only availavle in plot dc2
+set nolegend
+*set plainplot
+plot v(+22) plainplot
+set plainwrite
+write test.out v(+22) vss#branch dc1.v(/22) dc1.vss#branch
+unset nolegend
+set color0=white
+*unset plainplot ; required if 'set plainplot'
+plot vss2#branch vs v(22) title 'Series resistor: Drain current versus drain voltage' xlabel 'Drain voltage' ylabel 'Drain current'
+.endc
+
+.end
+
+
+
+
+

src/frontend/plotting/plotit.c

@@ -704,12 +704,14 @@ bool plotit(wordlist *wl, const char *hcopy, const char *devname)
     }
 
     if (!sameflag) {
-        plain = getflag(wl, "plain");
+        plain = getflag(wl, "plainplot");
     }
-    else if (getflag(wl, "plain")) {
+    else if (getflag(wl, "plainplot")) {
         plain = TRUE;
     }
 
+    plain = plain | cp_getvar("plainplot", CP_BOOL, NULL, 0);
+
     if (!wl->wl_next) {
         fprintf(cp_err, "Error: no vectors given\n");
         goto quit1;
@@ -724,8 +726,10 @@ bool plotit(wordlist *wl, const char *hcopy, const char *devname)
         wordlist* wli;
         for (wli = wl->wl_next; wli; wli = wli->wl_next) {
             d = vec_get(wli->wl_word);
-            if (!d)
+            if (!d) {
+                fprintf(stderr, "Error during 'plot': vector %s not found\n", wli->wl_word);
                 goto quit;
+            }
             if (vecs)
                 lv->v_link2 = d;
             else