如何在matlab上绘制3d不等式 [英] how to plot 3d inequalities on matlab

问题描述

我想在 MATLAB 中绘制一个以一组不等式为界的 3d 区域.

例如:

0 <= x <= 1sqrt(x) <= y <= 10 <= z <= 1 - y

我在本网站上找到了一个 2d 示例，但我不确定如何将其转换为 3d.

I want to plot a 3d region in MATLAB bounded from a set of inequalities.

For example:

0 <= x <= 1

sqrt(x) <= y <= 1

0 <= z <= 1 - y

I found a 2d example that someone has done on this site but I'm not sure how to convert that to 3d. How to plot inequalities.

Edit: From @Tobold's help I modified the code to restrict the points that are plotted to those that are defined by all three regions, but it plots only 2 or 3 points. It looks like the points in the vectors X1, Y1 and Z1 are right but for some reason its plotting only a few. Any ideas why it is only plotting a few points from the X1, Y1 and Z1 vectors instead of all of them?

[X,Y,Z]=meshgrid(0:0.1:1,0:0.1:1,0:0.1:1); % Make a grid of points between 0 and 1
p1=0.1; p2=0.2; % Choose some parameters
X1 = (X >= 0 & X <= 1) & (Y >= sqrt(X) & Y <= 1) & (Z >= 0 & Z <= 1 - Y);
Y1 = (X >= 0 & X <= 1) & (Y >= sqrt(X) & Y <= 1) & (Z >= 0 & Z <= 1 - Y);
Z1 = (X >= 0 & X <= 1) & (Y >= sqrt(X) & Y <= 1) & (Z >= 0 & Z <= 1 - Y);
ineq1 = (X >= 0 & X <= 1) * 2;
ineq2 = (Y >= sqrt(X) & Y <= 1) * 4;
ineq3 = (Z >= 0 & Z <= 1 - Y) * 8;
all = ineq1 & ineq2 & ineq3;
colors = zeros(size(X))+ineq1+ineq2+ineq3;
scatter3(X1(:),Y1(:),Z1(:),3,colors(:)','filled')

解决方案

I don't understand several things in the code that you wrote as modification of @Tobold's help. For example what are the parameters p1 and p2 doing in your code?

Anyway, The code plotting only the points of your grid satisfying all of your inequalities;

[X,Y,Z]=meshgrid(0:0.1:1,0:0.1:1,0:0.1:1);
ineq1 = (X >= 0 & X <= 1);
ineq2 = (Y >= sqrt(X) & Y <= 1);
ineq3 = (Z >= 0 & Z <= 1 - Y);
all = ineq1 & ineq2 & ineq3;
scatter3(X(all),Y(all),Z(all),'b','filled')

The result is brought in the following image.

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