How to save a numeric value in a specified location of a CSV file inside for loops?

I want to do this because otherwise I run out of memory to save the values in a matrix, as the dimensions of the matrix increases.

For example,

for a=1:10000
   for b=1:10000
      M(a,b)=rand;
   end
end

Here, the system runs out of memory as it can't store a 10000x10000 matrix.

So, I want to keep writing the (a,b)'th value inside the for loops into the (a,b)'th cell of a csv file (or an xls file, whatever). How do I do that?

I want something like this:

for a=1:10000
   for b=1:10000
      xlswrite1('file.xls',rand,a,b); % better if I can get a solution with csvwrite, as I prefer CSVs to work with
   end
end

But this obviously doesn't work. The error it gives is:

Error using evalin
Undefined function or variable 'Excel'.

Error in xlswrite1 (line 2)
Excel=evalin('caller','Excel');

Then when I add the following lines according to this article,

Excel = actxserver ('Excel.Application');
File='datafile.xls';
if ~exist(File,'file')
ExcelWorkbook = Excel.workbooks.Add;
ExcelWorkbook.SaveAs(File,1);
ExcelWorkbook.Close(false);

it gives this error:

Error using xlswrite1 (line 82)
Range argument must a string of Excel A1 notation.

Can anyone please suggest a simple solution? I can't find any from my online search so far.

Answer 1

[KSSV]

You can do this using dlmwrite. But I suggest you to write row by row instead of element by element.

N = 100 ;
M = zeros(N,N) ;
filename = 'test.csv';
for a=1:N
   for b=1:N
      M(a,b)=rand;
   end
   dlmwrite(filename,M(a,:),'-append')
end