plot3 out of loop

Question

Oday Shahadh 2020-6-9

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/545360-plot3-out-of-loop

评论： Oday Shahadh 2020-6-10

Can you please fix empty plot in below script

clear
close all
format long
theta=0:10:360;
rho=0:.5:2;
L=-2:0.5:2;
 X= cell(3,1) ; Y= cell(3,1);Z = cell(3,1) ;  
for i=1:length(L)
   for j=1:length(rho);
        for k=1:length(theta);
            [x,y,z]=pol2cart(theta(k),rho(j),L(i));
            X{i} = x ; Y{i} = y ; Z{i} = z ;            
        end
    end
end
figure(1)
hold on
plot3(X,Y,Z)

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Answer 1

David Hill 2020-6-9

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clear;
theta=0:10:360;
rho=0:.5:2;
L=-2:0.5:2;
[a,b,c]=meshgrid(theta,rho,L);
[x,y,z]=pol2cart(a,b,c);
plot3(x(:),y(:),z(:));

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David Hill 2020-6-10

It just converts x matrix into a column vector (reshaping to 1 dimension)

Oday Shahadh 2020-6-10

Very good job David

Can I ask another thing pls?

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Answer 2

Adam Danz 2020-6-9

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在 MATLAB Online 中打开

A critical missing bit of information is missing from your questions. An error is thrown by the last line in your quesiton.

Error using plot3
Not enough input arguments. 

This is because your plot3() inputs are cell arrays. It looks like your loops produce scalar values on each iteration so those values can be stored within a numeric array which will be much easier to use.

Your loops were overwriting the x,y,z values on each iteration of the j and k loops. The method below will store those values but it's up to you to make sure this makes sense in the context of whatever you're doing.

theta=0:10:360;
rho=0:.5:2;
L=-2:0.5:2;
% Numeric arrays, not cell arrays
% Also, preallocation to the correct size
X = nan(length(L), length(rho), length(theta)) ;
Y = X;
Z = X;   
for i=1:length(L)
   for j=1:length(rho)
        for k=1:length(theta)
            [x,y,z]=pol2cart(theta(k),rho(j),L(i));
            X(i,j,k) = x ; Y(i,j,k) = y ; Z(i,j,k) = z ;  % Store all of the value     
        end
    end
end

As for plotting, it's not clear how you would like to use these values. plot3() creates a 2D plot but the inputs cannot have more than 2 dimensions and the x y z values above have 3 dimensions.