How to add an additional legend that shows the dashing one is using?

Question

I am trying to plot two different functions into a single plot. Each function depends on R and r. I plot against r for different R's. So I end up with two different functions for all the different values of R. I use SwatchLegend to plot the legends of the different values of R. However, I also want to plot another legend that shows which dashing I am using for each function. Such that the final plot clearly shows which values I am using of R and that it is clear which dashing is of each function. My synthesized code is: First, I define the functions that I am using as

CYLINDER1[R_, r_] := 
  E^(-((2.789371726903078` BesselK[0, 0.010765343149384599` r])/
   BesselK[1, 0.010765343149384599` (2.125` + R)]));
SPHERE1[R_, r_] := 
  E^(-((3.002854381130314`*^8 E^(
    0.010765343149384599` (2.125` - r + R)) (2.125` + R))/(
   r (1.0765343149384598`*^8 + 10000000000/(2.125` + R)))));

Afterwards, I defined the values of R that I will vary, as well as the command that I will use to call the legends and placed them where I want. I also define some constants to create the dashing of my wish. And finally , I create a function to plot both functions.

RAD = {5, 15, 30, 80} ;
legrad[X_, Y_] := 
  Placed[SwatchLegend[{"5 \[Angstrom]", "15 \[Angstrom]", 
     "30 \[Angstrom]", "80 \[Angstrom]"}, 
    LabelStyle -> {FontSize -> 13}], {X, Y}];
l1 = 0.025;
l2 = 0.015;
d = 0.001;
s1 = l1/2;
s2 = l2/2;
C1g[X_, Y_, legX_, legY_] := 
  Plot[Evaluate@Table[ArcSinh[CYLINDER1[R, r]], {R, RAD}], {r, 0, X}, 
   PlotRange -> {-0.05 Y, Y}, PlotLegends -> legrad[legX, legY], 
   PlotStyle -> Dashing[{l1, s1, l1, s1, d, s1}]];
S1g[X_, Y_] := 
  Plot[Evaluate@Table[ArcSinh[SPHERE1[R, r]], {R, RAD}], {r, 0, X}, 
   PlotRange -> {-0.05 Y, Y}, 
   PlotStyle -> Dashing[{l2, s2, l2, s2, d, s2}]];

Finally I merge them with

CS1g[X_, Y_, legX_, legY_] := 
      Show[C1g[X, Y, legX, legY], S1g[X, Y], Frame -> True];

How and where do I add another legend to show the dashing and the functions (something like "--.-- Cylinder", "..-..- Sphere") Furthermore, since I am already asking, if I were to change the values of RAD={}. What can I do so I won't need to rewrite my labels?

Thanks in advance for the help.

Answer 1

You can use a LineLegend (with Dashing specs in the first argument) in one of the plots. Show combines legends from input plots intelligently.

Using a simpler example:

RAD = Range[3];
plot1 = Plot[Evaluate[Table[Sin[a x], {a, RAD}]], {x, 0, 2 Pi}, 
      PlotStyle -> Dashing[Tiny], 
      PlotLegends -> SwatchLegend[RAD, LegendLabel -> "RAD"]];

plot2 = Plot[Evaluate[Table[Cos[a x], {a, RAD}]], {x, 0, 2 Pi}, 
      PlotStyle -> Dashing[Medium], 
      PlotLegends ->  LineLegend[{Dashing[Tiny], Dashing[Medium]}, {"Sin", "Cos"}, 
          LegendLabel -> "Function"]];

Show[plot1, plot2]

You can also specify different positions for the two legends. For example, if we use

 PlotLegends -> Placed[SwatchLegend[RAD, LegendLabel -> "RAD", 
   LegendLayout -> "Row"], Top]

in plot1, Show[plot1, plot2] gives

Update: An alternative approach is to use a single hybrid legend with swatch and line elements, use it as the option setting for PlotLegends in one of the plots:

hybridlegend =  SwatchLegend[{## & @@ (ColorData[97] /@ Range[3]),
   Dashing[Tiny], Dashing[Medium]},
  {"rad 1", "rad 2", "rad 3", "Sin", "Cos"}, 
  LegendMarkerSize -> {Automatic, Automatic, Automatic , {30, 20}, {30, 10}}, 
  LegendMarkers -> {"Square", "Square", "Square", "Line",  "Line"}];

 Show[plot1, plot2]

Note: In version 9, you can use SwatchLegend[{Automatic, Automatic, Automatic, Dashing[Tiny], Dashing[Medium]}, ...] inside Plot and it picks the right colors for the swatch markers.