# How can I show constraints on parameters in 3D plot? [closed]

How can I exclude a region in a 3D plot?

I have done it for a Density plot, but for the 3D case, it seems difficult to exclude a region (with a certain relation between two main parameters). In fact, the 3D plot is for a relation in terms of "a" and "b", and each one of these parameters has a limitation. I want to denote the area of banned values of "a" and "b" (which is an inequality relation between these parameters) by a red boundary in the main 3D plot.

## closed as off-topic by Sektor, m_goldberg, gwr, José Antonio Díaz Navas, LCarvalhoMar 9 '18 at 20:47

This question appears to be off-topic. The users who voted to close gave this specific reason:

• "This question cannot be answered without additional information. Questions on problems in code must describe the specific problem and include valid code to reproduce it. Any data used for programming examples should be embedded in the question or code to generate the (fake) data must be included." – Sektor, m_goldberg, gwr, José Antonio Díaz Navas, LCarvalho
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• It is easier to help, if you provide code with your own attempt as a starting point and an example figure illustrating what you want to achieve. – Johu Mar 9 '18 at 10:58
• Use the option RegionFunction for Plot3D as shown in the documentation. – gwr Mar 9 '18 at 11:07
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Here is a simple example of how you might do it using RegionFunction. As proxy for a 3D-Plot I am using the binormal density from another post:

dist = BinormalDistribution[ {0, 0}, {1, 1}, 0.7 ] (* may sound familiar :) *)

Show@{
Plot3D[ PDF[dist, {x, y}], {x, -2, 2}, {y, -2, 2},
RegionFunction -> Function[{x, y}, (x + y > 1) || (x + y < -1)],
PlotRange -> All
],
Plot3D[  PDF[dist, {x, y}], {x, -2, 2}, {y, -2, 2},
RegionFunction -> Function[{x, y}, x + y <= 1 && x + y >=  -1],
PlotStyle -> Red
]
}


• Note that for a good result I negated the exlusions for the primary plot. – gwr Mar 9 '18 at 11:33
• How can I bring a part of my calculations here? Sorry, I'm a beginner :/ – Perfect Fluid Mar 9 '18 at 14:20