store variables in a for loop

Hello,

i m trying to obtain a set of coordinates for this:

function [x, y] = gencircle(xo,yo,r,N)
x=(xo+r*cos(theta))';
y=(yo+r*sin(theta))';

clear all

xo=[1 2 3 4 5 6 7 8];
yo=[-1 -0.5];
r=0.01;
N=10;
theta=2*pi/N*(1:N+1);
th=0.00235;


for j=1:length(yo)
    for i=1:length(xo)
        [xout(:,i), yout(:,j)]=gencircle(xo(i),yo(j),r,N)
        [xin(:,i), yin(:,j)]=gencircle(xo(i),yo(j),r-th,N)
    end
end


for j=1:length(yo)
    for i=1:length(xo)
        aa=[xout(:,i),yout(:,j)]
    end
end

how can i store the vector aa for each loop?

Thanks

Answer 1

[Sriram Tadavarty]

Hi Davide,

You can make the following modification to the code as shown below, which stores all the loop iteration values in the variable aa:

clear all

xo=[1 2 3 4 5 6 7 8];
yo=[-1 -0.5];
r=0.01;
N=10;
theta=2*pi/N*(1:N+1);
th=0.00235;


for j=1:length(yo)
    for i=1:length(xo)
        [xout(:,i), yout(:,j)]=gencircle(xo(i),yo(j),r,theta);
        [xin(:,i), yin(:,j)]=gencircle(xo(i),yo(j),r-th,theta);
    end
end

aa = zeros(size(xout,1),2,length(yo)*length(xo)); % Initialize the variable
tmp = 1;
for j=1:length(yo)
    for i=1:length(xo)
        aa(:,:,tmp)=[xout(:,i),yout(:,j)];
        tmp = tmp+1;
    end
end

% aa will be a variable of size length(xout) x 2 x (loop iterations)
% loop iterations here is equal to the product of length(yo) and length(xo) (implies 16)
% Each iteration value can be accessed by indexing from 3rd dimension,
% implies for example fifth iteration can be accessed with aa(:,:,5)

function [x, y] = gencircle(xo,yo,r,theta)
x=(xo+r*cos(theta))';
y=(yo+r*sin(theta))';
end

Hope this helps.

Regards,

Sriram

[Stephen23]

It is recommended to preallocate aa before the loops:

https://www.mathworks.com/help/matlab/matlab_prog/preallocating-arrays.html

[Sriram Tadavarty]

Yes. Updated the answer with the variable pre-allocation.

[Davide Cerra]

incredibly useful, thanks!

[Sriram Tadavarty]

Please do accept the answer, if helped