plot curve with nan's

pub/lib/plot.cpp

@@ -300,7 +300,7 @@ namespace {
         public:
             double xd; // data point
             double yd;
-            int code; // 0=valid, 1=below, 2=above, 3=off_range
+            int code; // -1=nan 0=valid, 1=below, 2=above, 3=off_range
             CP2 P; // plot point
         };
 
@@ -311,7 +311,9 @@ namespace {
                 vector<CPt> ret(x.size());
                 for (size_t i=0; i<x.size(); ++i) {
                     double xp = plot->X.pc(x[i]);
-                    if (y[i]<plot->Y.inf)
+                    if (std::isnan(y[i]))
+                        ret[i] = {x[i], y[i], 1, {xp, NAN}};
+                    else if (y[i]<plot->Y.inf)
                         ret[i] = {x[i], y[i], 1, {xp, NAN}};
                     else if (y[i]>plot->Y.sup)
                         ret[i] = {x[i], y[i], 2, {xp, NAN}};