how to predefine a matrix with one unknown dimension

hey everybody I am interested in predefining a matrix with unknown dimension. I know that the matrix should have 15 rows (number of iterations), but the number of columns (time stages) depends on a stop condition in the code, and hence can't be known in advance. can I create a general definition like v=[]; but for a matrix with one known dimension? In addition, is it possible to create a zero matrix with 1 unknown dimension?

thanks!

[Eliraz Nahum]

Thank you all. Both ways are good and I even learned some new elegant things.

Answer 1

[Matt J]

No, all the dimensions of a matrix must be explicitly defined. What I often do in those cases is pre-define a cell array,

 C=cell(1,N)

with a conservatively large N. Then, as the loop runs, accumulate the data in a sequence of cells,

   for  i=1:N

     C{i}=next_column;

     if stop_condition
       break;
     end

   end

Later, you can just assemble the cells into a matrix with,

 A=cell2mat(C);

and the empty cells will be ignored.

Answer 2

[Image Analyst]

Just define a matrix that's well large enough to hold all your numbers, like a few million elements or whatever.

v = zeros(15, 1000000);

Then do whatever you need to do assigning rows and columns in v, then, if you've kept track of the max column number, you can simply crop the array

v = v(:, maxColumn);