pol2cart in loop and pre-allocating

hi all,

how can I put [x,y,z]=pol2cart(theta,rho,z), in tripple loop for different values of heta,rho,z, as well how to pre allocate [x,y,z]?

Regards

Answer 1

[KSSV]

You need not preallocate (x,y,z) when you use the function.....If you want to run it thrice, you can do the following.

X = cell(3,1) ; Y = cell(3,1);Z = cell(3,1) ;  
for i = 1:3
    [x,y,z]=pol2cart(theta{i},rho{i},z{i}) ; 
    X{i} = x ; Y{i} = y ; Z{i} = z ; 
end

If all the size of theta, rho, z are same. You can use matrices instead of cells.

N = length(theta) ; 
X = zeros(N,3) ; Y = zeros(N,3); Z = zeros(N,3) ; 
for i = 1:3
    [x,y,z]=pol2cart(theta(:,i),rho(:,i),z(:,i)) ; 
    X(:,i) = x ; Y(:,i) = y ; Z(:,i) = z ; 
end

[Oday Shahadh]

clear
close all
format long
theta=0:45:360;
rho=0:.5:2;
L=-2:2;
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)
plot3(x,y,z);hold on

why can not plot the results?

[KSSV]

clear
close all
format long
theta=0:45:360;
rho=0:.5:2;
L=-2:2;
X = cell(3,1) ; Y = cell(3,1);Z = cell(3,1) ;  
figure
hold on
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 ; 
            plot3(x,y,z,'.')
        end
    end
end

[Oday Shahadh]

empty plot also!

[Oday Shahadh]

it must be something like the attached plots

[KSSV]

Check does x, y, z have any values...

[Oday Shahadh]

yes there is a values ,it works just in case that insert plot command inside the loop with ('.')

I need to put the plot outside,pls

thanks

Answer 2

[David Hill]

No need for loop or for preallocating when you just execute for arrays of theta,rho, and Z.

theta=linspace(0,pi,100);
rho=linspace(0,10,100);
Z = linspace(10,100,100);
[x,y,z]=pol2cart(theta,rho,Z);