Exporting EPS figures with dashing from ListPlot

Question

I am having difficulties exporting EPS figures. If I use the LineLegend option to create a dashed or a dot-dashed line, it seems ok in Mathematica 9.0 e.g.:

But the problem came out when the figure was expoted to EPS e.g.,

I use the following Mathematica code

G1 = ListPlot[{
      Table[{(i - 1) h, ρf[u, (i - 1) h, RKuOm, FB][[4, 4]]}, {i, 1, n - 1}],
      Table[{(i - 1) h, ρf[u, (i - 1) h, RKuOm, FB][[3, 3]]}, {i, 1, n - 1}], 
      Table[{(i - 1) h, ρf[u, (i - 1) h, RKuOm, FB][[2, 2]]}, {i, 1, n - 1}]
      }, 
      PlotRange -> All, MaxPlotPoints -> Infinity, Joined -> True, 
      PlotLegends -> Placed[LineLegend[{Directive[Purple, Thickness[0.14]], 
       Directive[Blue, Thickness[0.14], Dashed], Directive[Red, Thickness[0.14], 
       DotDashed]}, {Style["\!\(\*SubscriptBox[\(ρ\), \(44\)]\)", 22, Bold], 
       Style["\!\(\*SubscriptBox[\(ρ\), \(33\)]\)", 22, Bold], 
       Style["\!\(\*SubscriptBox[\(ρ\), \(22\)]\)", 22, Bold]}, 
      LegendMarkerSize -> {{35, 8}}], {{0.82, 0.4}}], AspectRatio -> 0.8, 
      PlotStyle -> {{Purple, Thickness[0.012]}, {Blue, Thickness[0.014], 
       Dashed}, {Red, Thickness[0.013], DotDashed}},  Frame -> True, 
      FrameStyle -> Directive[Thick, 15],
      FrameLabel -> {Style["\!\(\*SubscriptBox[\(ω\), \(1\)]\)t", 18], None}, 
      Epilog -> {Inset[Style["(a)", 24, FontFamily -> "Times", Bold], {6, 0.95}], 
               Inset[Style["G=0.1", 24, FontFamily -> "Times", Bold], {41.5, 0.61}]}]

Export["D:\\fermion.eps",G1,"EPS"];`

So, my question: why the style of the lines change? And how to solve?

Many thanks in advance.

Answer 1

Here is a more simple example showing the same effect:

 G1 = ListPlot[
      Table[{i , Sin[i j Pi/50]}, {j, 3}, {i, 50}], PlotRange -> All, 
      Joined -> True, AspectRatio -> 0.8, 
      PlotStyle -> {{Purple, Thickness[0.012]}, {Blue, Thickness[0.014], 
                    Dashed}, {Red, Thickness[0.013], DotDashed}}]
 Export["test1.eps", G1, "EPS"];

The problem turns out to be that postscript is putting linecaps on all the little segments that are proportional to the line thickness. If you look close you see the lines are "dashed" but the segments run together. (Screendump from Acrobat conversion of the eps)

The fix is to specify CapForm[] :

 G2 = ListPlot[
     Table[{i , Sin[i j Pi/50]}, {j, 3}, {i, 50}], PlotRange -> All, 
      Joined -> True, AspectRatio -> 0.8, 
      PlotStyle -> {{Purple, Thickness[0.012]}, {Blue, Thickness[0.014], 
        CapForm["Butt"], Dashed}, {Red, Thickness[0.013], DotDashed}}]
       Export["test3.eps", G2, "EPS"];

Oddly CapForm["None"] doesn't work.

Acrobat conversion of the eps:

Note the effect carried over to the second dashed line even though I only put it on the first.

Incedentally knowing this we can get (IMO) nicer dashing in eps with round linecaps and with explicit dashing specified:

  PlotStyle -> {{Purple, Thickness[0.012]}, {Blue, Thickness[0.014], 
       CapForm["Round"], Dashing[{0.014 2, 0.014 2}]}, {Red, 
         Thickness[0.013], Dashing[{1*^-10, 0.014 2, 0.014 2, 0.014 2}]}}

note the "really small" 10*^-10 dash length gives a perfect circle in the eps plot. ( 0 does not work as well ). Be aware the round caps are not supported by many (most?) export formats however.