Plot 3D Graph and make level curves

2021 4 22
3 个回答
回答已采纳
更新时间：2021 5 1
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Hi
I have 3 vectors, where:
X is a vector of numbers;
Y is a vector of numbers;
Z is a function that depends on X and Y (i.e)
Z = 4.6597*x.^2 + 2.6897*x.*y - 0.023578*x + 8.1189*y.^2 - 1.9553*y - 1.2304;
I want to plot a 3D curve and I am not succeding. Can someone help me please? Thanks

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Star Strider
Star Strider 2021-4-23
编辑：Star Strider 2021-4-23

1 个投票

Use the plot3 function.
If you then want it as a 2D plot, use the view function to rotate it.
EDIT — (23 Apr 2021 at 03:17)
I was intending that to use any of the q3D plotting functions, the vectors need to be transformed into matrices first, and then transformed back into vector to use plot3:
X = ...;
Y = ...;
[Xm,Ym] = ndgrid(X,Y);
Zfcn = @(x,y) 4.6597*x.^2 + 2.6897*x.*y - 0.023578*x + 8.1189*y.^2 - 1.9553*y - 1.2304;
Zm = Zfcn(Xm,Ym);
figure
plot3(Xm(:), Ym(:), Zm(:))
grid on
.

8 个评论
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Bryan Ambrósio
Bryan Ambrósio 2021-4-23
Great man, thank you so much.
Star Strider
Star Strider 2021-4-23
编辑：Star Strider 2021-4-23
My pleasure!
Bryan Ambrósio
Bryan Ambrósio 2021-4-23
编辑：Bryan Ambrósio 2021-4-23
I am also trying to use
contour(Xm, Ym, Zm), it worked just fine
But i want to be sure if the Z axis is beeing cutted in points 1, 2, 3, ..., 8.
How can i make sure of that?
And i think it will be better if in figure of contour the ordened pair appears only as a 'x' or 'o', and not the entire line
Star Strider
Star Strider 2021-4-23
If you want to specify those contours:
contour(Xm, Ym, Zm, (1:8))
The extra parentheses are not strictly necessay, I added them for clarification.
X = ...;
Y = ...;
[Xm,Ym] = ndgrid(X,Y);
Zfcn = @(x,y) 4.6597*x.^2 + 2.6897*x.*y - 0.023578*x + 8.1189*y.^2 - 1.9553*y - 1.2304;
Zm = Zfcn(Xm,Ym);
figure
contour(Xm, Ym, Zm, (1:8))
axis('equal')
If you want to label the contours:
contour(Xm, Ym, Zm, (1:8), 'ShowText','on')
That worked when I tried it with my own set of vectors.
Bryan Ambrósio
Bryan Ambrósio 2021-4-30
编辑：Bryan Ambrósio 2021-4-30
Hi, im sorry to bother you again, but now i need to make the same plots, but:
X, Y and Z are vector (not function anymore), how do i do that?
I have tried:
X = ...;
Y = ...;
Z = ...;
[Xm,Ym, Zm] = ndgrid(X,Y,Z);
figure
contour(Xm, Ym, Zm, (1:8))
axis('equal')
but its not working
Star Strider
Star Strider 2021-4-30
No worries!
Do this instead —
X = ...;
Y = ...;
Z = ...;
xv = linspace(min(X),max(X),numel(X));
yv = linspace(min(Y),max(Y),numel(Y));
[Xm,Ym] = ndgrid(xv,yv);
Zm = griddata(X,Y,Z,Xm,Ym);
figure
contour(Xm, Ym, Zm, (1:8))
axis('equal')
That should work.
.
Star Strider
Star Strider 2021-5-1
As always, my pleasure!

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