Having problems with saving vectors in a loop

I want to save the vectors "c" and "r" for each iteration in the loop(code below). Any suggestions please?

lines = houghlines(rotI,theta,rho,P,'FillGap',5,'MinLength',25);
for k = 1:length(lines)
   xy = [lines(k).point1; lines(k).point2];
   a = (xy-1);
   r = (xy+1);
   c = [a(1) a(2) r(2) r(1)];
   r = [a(3) a(4) r(4) r(3)];
end

The two vectors "c" and "r" are both 1x4 in the first iteration. When I tried using "c(k),r(k)" it returns the error: "In an assignment A(I) = B, the number of elements in B and I must be the same". And when I used "c(k,:),r(k,:)", it gave me the error message: "Subscripted assignment dimension mismatch". The thing is "c" and "r" will increase in size at each loop iteration; and want it to be such that when k=1: c&r = 1x4 k=2: c&r = 2x4....k=n: c&r = nx4 How do I save c & r? Please help.

Answer 1

[Aliyu Abdu]

Since the vectors "c & r" change row size in each loop iteration:

c = zeros(length(lines),4); %Initialization(in my case n is constant=4)
r = zeros(length(lines),4);
for k = 1:length(lines)
 xy = [lines(k).point1; lines(k).point2];
 a = (xy-2);
 b = (xy+2);
 c(k,:) = [a(1) a(2) b(2) b(1)]*1^k;%Simply to introduce "k" in the... %...assignment.
 r(k,:) = [a(3) a(4) b(4) b(3)]*1^k;
end

[Aliyu Abdu]

Thanks to: http://www.mathworks.com/matlabcentral/answers/contributors/869436-doug-hull

Answer 2

[Thomas]

This video should help:

http://blogs.mathworks.com/videos/2007/08/20/matlab-basics-video/

Eg>

      for jj = 1:500
    B(jj)=rand(1);
      end

B will be a vector of size 500

In you case it should be easy to save c and r as vector using c(k),r(k) or if you have those as arrays as c(k,:) and r(k,:)

[Aliyu Abdu]

The two vectors "c" and "r" are both 1x4 in the first iteration.

When I tried using "c(k),r(k)" it returns the error: "In an assignment A(I) = B, the number of elements in B and I must be the same".

And when I used "c(k,:),r(k,:)", it gave me the error message: "Subscripted assignment dimension mismatch".

The thing is "c" and "r" will increase in size at each loop iteration;

and want it to be such that when k=1: c&r = 1x4

k=2: c&r = 2x4

.

.

k=n: c&r = nx4

How do I save c & r? Please help.