problem with plotting a 3D graph
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Hi,
Please I need help to get the following code working:
Blue = [2 3 4 5 6]';
Green = [2 4 6 10 12]';
Red = [3 6 9 12 15]';
BL = Blue(1:end);
GR = Green(1:end);
RD = Red(1:end);
join = [];
for i = 1:GR
for j = 1:RD
join(i+1,j+1) = BL;
end;
end;
surf(join)
When I ran the code in Matlab, I got the following error message: "??? Subscripted assignment dimension mismatch." My intention was to plot the data in 3D.
Thanks
James
1 个评论
Azzi Abdelmalek
2012-8-9
why
BL = Blue(1:end);
you can writte
BL = Blue
采纳的回答
Star Strider
2012-8-9
编辑：Star Strider
2012-8-9
If all you want to do is plot Blue as a function of Green and Red, I suggest simply:
scatter3(GR, RD, BL, 'p')
to plot them as five-pointed stars, or:
stem3(GR, RD, BL)
if you want to know where Blue's Green and Red coordinate locations are as well.
If you want to plot join as a surface, you need to be more specific, and calculate join differently. I refer you to meshgrid.
One problem is with the way you define join in your loop. I don't understand what you want to do, but to avoid the error you got, I suggest changing it to something like:
join = [];
for i = 1:max(GR)
for j = 1:max(RD)
join(i+1,j+1,:) = BL;
end
end
although you will have to change your code significantly to plot your data as a surface.
6 个评论
James
2012-8-9
Star Strider
2012-8-9
编辑：Star Strider
2012-8-9
Well, you want to create a surface out of 3 [5 x 1] vectors. That's a lot to ask of them!
The best I can come up with is:
Blue = [2 3 4 5 6]';
Green = [2 4 6 10 12]';
Red = [3 6 9 12 15]';
P = [ones(size(Blue)) Green Red]\Blue;
[XG YR] = meshgrid(Green, Red);
ZB = P(1) + P(2)*XG + P(3)*YR;
figure(32767)
surf(XG, YR, ZB)
xlabel('Green')
ylabel('Red')
zlabel('Blue')
grid on
It creates a regression surface and a linear regression of Blue on [Green Red]. It is an exact fit, so it seems an appropriate solution. If there's a known functional relationship between your variables, use that instead.
James
2012-8-10
Star Strider
2012-8-10
P are the parameters vector calculated by solving this matrix equation:
[1 G R]*P = B
A bit less cryptically, it's a multiple linear regression (more formally implemented by the regress function in the Statistics Toolbox). The way I interpreted your code, I am assuming that Blue is a linear function of Green and Red (along with a constant term, necessary in such situations, something like the y-intercept in bivariate regression). You don't necessarily have to use the constant term in your situation, so feel free to simply regress Blue against Green and Red without the constant term if you like. The fit may not be as good, however.
MATLAB uses the backslash ‘\’ operator to implement a least-squares solution to such equations. It's quite useful.
James
2012-8-12
Star Strider
2012-8-12
My pleasure!
I learned a lot in the process as well.
更多回答（2 个）
Azzi Abdelmalek
2012-8-9
编辑：Azzi Abdelmalek
2012-8-9
%if you want plot a 3D graph with x axis Blue and Yaxis Green and corresponding data : example : z=rand(5,5)
Blue = [2 3 4 5 6]';
Green = [2 4 6 10 12]';
z=rand(5,5)
surf(Blue,Green,z)
Kartik Verma
2020-12-1
0 个投票
Take two vectors, x and y, of your choice of length 50. Consider a function
z=x^2+y^2-xy
Make a 3D surface plot for x,y and z with proper axis titles, legends etc.
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