Labeling points of intersection between plots

There are several answers where Mathematica used mesh points to show graphically where curve intersections exist.

Is there a way to include the actual point values (maybe they are simply labeled as a, b, c ...) and then the actual value is displayed on the right of the graphic?

Here is the specific example I am working.

Plot[{Cos[x],(1/2)^x},{x,-1,11},
PlotPoints->84,
MaxRecursion->9,
MeshFunctions->{Cos[#1]-(1/2)^#1&},
Mesh->{{0}},
MeshStyle->Directive[Red,PointSize[Large]]]
• You can put Graphics[Text[#, #] & /@ coords] to the Show or just Text part to the Epilog. – Kuba Sep 11 '13 at 6:09
• @Kuba ... and with small offset on the coordinate part of Text, it's positioned next to the point itself, not on top of it. – kirma Sep 11 '13 at 6:41
• lines meet at solutions of two lines equations..may be you want to find solutions first and them use Text as suggested to get only relevant info. – Rorschach Sep 11 '13 at 6:55

opts = {ImageSize -> 500, PlotRange -> {{-5, 15}, All}, PlotPoints -> 84,
MaxRecursion -> 9, MeshFunctions -> {Cos[#1] - (1/2)^#1 &}, Mesh -> {{0}},
MeshStyle -> {Directive[Red, PointSize[Large]]}};

You may be interested in the fact that Mesh solution is good for visulatisation purposes but it seems that coordinates given with this method are only approximation.

Also there are double points, one for each curve and each aproximation is independent what may result in different coordinates.

Taking your example let's label those points:

(Plot[{Cos[x], (1/2)^x}, {x, -1, 11}, Evaluate@opts] // Normal
) /. Point[x_] :> ({Point@x,
Text[Style[NumberForm[#, {Infinity, 2}], Bold, Black, 15] &@x
, x + {0, .5 - RandomReal[]/2}]})

It basically replaces points with points + labels. Labels are with random offset so you can see what I was reffering to. Normal is in order to get rid of the GraphicsComplex. As you can see, the mesh point near $y$ axis has different coordinates :)

Edit So at the end I would use NSolve based solution like in the first link you've provided:

After all I forgot you asked for the legend next to the plot :)

points = {x, Cos[x]} /. NSolve[Cos[x] == (1/2)^x && -1 < x < 11, x];
names = FromCharacterCode /@ (Range[Length@points]+96)
{"a", "b", "c", "d", "e"}
Row[{
Plot[{Cos[x], (1/2)^x}, {x, -1, 11}, Evaluate@opts,
Epilog -> (Text[Style[#, 20], #2 + {0, .2}] & @@@ Transpose[{names, points}])
]
,
}] • I know it's an old question / answer, but I need to understand why, in your first solution, there are double coordinates at each intersection point? – Conrad Sep 8 '15 at 15:56
• @Conrad I'm not sure but it seems it is what I;ve said. Mesh points are generated separately for each curve, maybe to be sure that everything is covered if one curve is problematic or something. – Kuba Sep 8 '15 at 18:42
• Ok, so your second solution (using NSolve) is preferable. But how would you manage intersection with several curves (Cos[x], Sin[x], Tan[x])? The syntax would become much more complex? – Conrad Sep 9 '15 at 12:49

DisplayFunction

Using a custom DisplayFunction that injects labels as locators for the mesh points:

ClearAll[displayF]
displayF[offset_: {20, 20}] := (Normal[#] /.
p : {__Point} :> (Point /@ DeleteDuplicates[p[[All, 1]],
Round[#, .1] == Round[#2, .1] &]) /.
Point[x_] :> {Point[x], Locator[Offset[offset, x],
Framed[Column @ Round[x, .0001], FrameStyle -> None,
Background -> Opacity[.5, Yellow]]]} &);

Examples:

Plot[{Cos[x], (1/2)^x}, {x, -1, 11}, PlotPoints -> 84,
MaxRecursion -> 9, MeshFunctions -> {Cos[#1] - (1/2)^#1 &},
Mesh -> {{0}}, MeshStyle -> Directive[Red, PointSize[Large]],
PlotRangeClipping -> False, ImageSize -> 600, ImagePadding -> 70,
DisplayFunction -> displayF[]] Plot[{x Sin[x], x Cos[x]}, {x, -1, 11}, PlotPoints -> 150,
MaxRecursion -> 9, MeshFunctions -> {# Sin[#] - # Cos[#] &},
Mesh -> {{0}}, MeshStyle -> Directive[Red, PointSize[Large]],
PlotRangeClipping -> False, ImageSize -> 600, ImagePadding -> 70,
DisplayFunction -> displayF[]] Perhaps ugly but may achieve what you want:

p = Plot[{Cos[x], (1/2)^x}, {x, -1, 11}, PlotPoints -> 84,
MaxRecursion -> 9, MeshFunctions -> {Cos[#1] - (1/2)^#1 &},
Mesh -> {{0}}, MeshStyle -> Directive[Red, PointSize[Large]],
ImageSize -> 300]

Extract intersection points (which as described are approximates with duplicates):

intp = Extract[p[[1, 1]], List /@ p[[1, 2, 2, 1, 2, 1]]]

"Clean" and sort (by removing "same" x value) and create labels:

sorted = Chop[#, 10^(-8)] & /@
SortBy[DeleteDuplicates[intp,
Chop[#1[] - #2[], 10^(-4)] == 0 &], #[] &]
labels = FromCharacterCode /@ (96 + Range[Length[sorted]])

Display:

Row[{
Show[p,
Graphics[ 