# Add lines to 3D Plot

GROUPS:
 How can I add lines that demarcate the different regions of the following 3D plot like [a > 0, c > 0], [a = 0, c > 0] etc.?Plot3D[1/(1 + E^(-a - c)), {a, -8, 8}, {c, -8, 8}]Thanks in advance!
4 years ago
6 Replies
 You may find the follwing helpful. (1) Drawing lines in 3D plots: http://mathematica.stackexchange.com/questions/20479(2) Various contour plot and marking planes inside 3D plots: http://mathematica.stackexchange.com/search?q=planes+in+3D+plot
4 years ago
 thanks for the references. I have looked at them but I still don't know how to solve the problem. To give you an idea of what I have in mind I have added the lines in paint to the diagram. What I want to know is how to make something similar in mathematica directly.
4 years ago
 Vitaliy Kaurov 3 Votes pl1 = Plot3D[1/(1 + E^(-a - c)), {a, -8, 8}, {c, 0, 8},     Mesh -> {{0}, {0}}, PlotStyle -> None,     MeshStyle -> Directive[Thick, Red]]; pl2 = Plot3D[1/(1 + E^(-a - c)), {a, -8, 8}, {c, 0, 8},     MeshFunctions -> {#1 + #2 &}, Mesh -> {{0}, {0}},     PlotStyle -> None, MeshStyle -> Directive[Thick, Red]]; pl3 = Plot3D[1/(1 + E^(-a - c)), {a, -8, 8}, {c, -8, 8},     Mesh -> {{0}, {0}}, MeshFunctions -> {#2 &}, PlotStyle -> None,     MeshStyle -> Directive[Thick, Red]];pl4 = Plot3D[1/(1 + E^(-a - c)), {a, -8, 8}, {c, -8, 8},    PlotStyle -> Directive[Yellow, Specularity[White, 20]],    MeshStyle -> Opacity[.5], PlotPoints -> 40];Show[pl3, pl1, pl2, pl4]