Using Mesh in ContourPlot to find intersections not working

Question

This old answer by @Silvia uses Mesh to find intersections of curves. Unfortunately, it doesn't seem to work in v13.2. For example (based on @JasonB's comment to that answer):

Clear[f, g]
f[x_, y_] := -Cos[y] + 2 y Cos[y^2] Cos[2 x];
g[x_, y_] := -Sin[x] + 2 Sin[y^2] Sin[2 x];
ContourPlot[{f[x, y] == 0, g[x, y] == 0}, {x, -7/2, 4}, {y, -9/5, 21/5},
  MeshFunctions -> {f[#1, #2] - g[#1, #2] &}, Mesh -> {{0}},
  MeshStyle -> Directive[Red, PointSize[Large]]]

There should be red points at the intersections. Any thoughts on how to get this working? What changed?

I also test v11.3 (work),v12.3( not work) , Something must be changed in v12. — cvgmt, Dec 23 '22 at 08:40

score 12 · Accepted Answer · answered Dec 23 '22 at 03:08

12

We can use two MeshFunctions {f[#1, #2] &, f[#1, #2] - g[#1, #2] &}

ContourPlot[{f[x, y] == 0, g[x, y] == 0}, {x, -7/2, 4}, {y, -9/5, 
  21/5}, MeshFunctions -> {f[#1, #2] &, f[#1, #2] - g[#1, #2] &}, 
 Mesh -> {{0}}, MeshStyle -> Directive[Red, PointSize[Large]]]

answered Dec 23 '22 at 03:08

cvgmt

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Thanks! I wonder what changed. – Chris K Dec 23 '22 at 03:20
Even a dummy first function like MeshFunctions -> {0 #1 &, f[#1, #2] - g[#1, #2] &} seems to work. – Chris K Dec 23 '22 at 03:36
@ChrisK It is also curious to me that {0 &, f[#1, #2] - g[#1, #2] &} also work. – cvgmt Dec 23 '22 at 03:48

Using Mesh in ContourPlot to find intersections not working

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