how can we plot this function as 3d with matlab?
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how can we plot this fucntion as 3d with matlab? I tried surf and ezplot to plot function. but they didnt work. thanks for help.
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Matt Tearle
2012-9-12
0 个投票
Aww, cute.
The reason you can't use surf or ezplot is that these are not designed for this kind of equation. To use surf you need to have a surface defined as z = f(x,y). You have g(x,y,z) = 0. If you could rearrange that into z = f(x,y), you could use surf, but the equation you have doesn't really allow that.
So... instead, go back to the definition of the surface as g(x,y,z) = 0. Think of this as a particular isosurface of the function g(x,y,z) (with isosurface value of 0).
To make a surface in MATLAB from that kind of setup, you need (surprise, surprise) isosurface. Look in the documentation at the examples for isosurface. They will guide you through the visualization.
The one thing you need that isn't in the isosurface doc is to create the data to plot. (The examples do [x,y,z,v] = flow; which creates the data from a canned routine for a specific example.) So:
- You need to create 3 3-D arrays for x, y, and z, in the given range -- hint: linspace and meshgrid.
- Then you need to evaluate the function g(x,y,z) at each of those x, y, z locations: V = (X.^2+9*Y.^2/4+Z.^2-1).^3 - X.^2.*Z.^3 (etc)
Now you have the data, you can plot, using the examples in the isosurface documentation.
You'll "love" the result. Haha. I'm so funny.
6 个评论
murat can
2012-9-12
Sean de Wolski
2012-9-12
Here is some help with (1)
[X,Y,Z] = meshgrid(linspace(-3,3,25));
Azzi Abdelmalek
2012-9-12
编辑：Azzi Abdelmalek
2012-9-12
the question asked was to plot X.^2+9*Y.^2/4+Z.^2-1).^3 - X.^2.*Z.^3=0 which don't correspond to the answer. you must solve the equation before ploting
Sean de Wolski
2012-9-12
@Azzi - no you don't!
isosurface is essentially a three dimensional contour plot. When you set the threshold value to zero, it will draw the isosurface at that interface thus automagically solving the equation for you :)
Azzi Abdelmalek
2012-9-12
Ok Sean, I widhdraw
更多回答（3 个）
Azzi Abdelmalek
2012-9-12
编辑：Azzi Abdelmalek
2012-9-12
sol=[];
for k=-3:0.1:3
for m=-3:0.1:3
x=[k m];
a=x(1)^2+x(2)^2*9/4-1;
v=[1 0 3*a 0 + 3*a^2 0 a^3 ];
z=roots(v);
z=z(imag(z)==0);
n=length(z);
if n>0
xyz=[repmat(x(1:2),n,1) z];
sol=[sol;xyz];
end
end
end
plot3(sol(:,1),sol(:,2),sol(:,3))
murat can
2012-9-12
3 个评论
murat can
2012-9-12
Sean de Wolski
2012-9-12
编辑：Sean de Wolski
2012-9-12
You don't need to define X,Y,Z,V as syms since they won't be syms but rather double arrays....
Removing that line, it works for me.
murat can
2012-9-12
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