fprintf in a for-loop

Hi,

I'm looking for a way to make my code faster. I'm facing the following problem:

I have a for-loop of 1:length(events). If the event == 1 the event and venue of the event is written to a text file. However, as the length of events is quite large, it takes some time to write the entire text file. I was wondering if there is a way to first store the array first and write it to the text file once the entire for-loop has been processed?

This is my code:

for f=events
  fprintf(fileid, ' Event%03d:  ' , f);
  counter=1;
     for v= venue_name
         if event(f)==1
              if counter==1
                  fprintf(fileid, '  X(%04d,%s) ',event(f),venue_name{v});
                  counter=counter+1;
              else
                  fprintf(fileid, ' + X(%04d,%s) ',event(f),venue_name{v});
              end
         end
      end
end

Can anyone help me with adapting this code such that it just writes the datafile at the end instead of once every iteration?

Answer 1

[Jan]

The runtime of the code is not the bottleneck, but the disk access. Therefore creating the large string at first has the additional disadvantage, that a lot of RAM must be allocated.

Most likely using an efficient buffering is more useful. How do you open the file? Try:

fileid = fopen(FileName, 'W');  % Uppercase!

Some small improvements of the code:

for f = events
  fprintf(fileid, ' Event%03d:  ', f);
  if event(f)==1  % Move outside the "v" loop
    first = true;
    for v = venue_name   % ??? 1:numel(venue_name) ???
       if first
         fprintf(fileid, '  X(%04d,%s) ',event(f),venue_name{v});
         first = false;
       else
         fprintf(fileid, ' + X(%04d,%s) ',event(f),venue_name{v});
       end
     end
  end
end

[Bas]

Thanks this saves me about 15% time already. I opened it with the 'w' instead of 'W'. Do you have any other solutions to improve even more?

[Jan]

Please explain, if you really mean "for v = venue_name" and "venue_name{v}". This looks strange. The same for "for f = events" together with "event(f)".

[Bas]

Yes, it's the name of a decision variable which will later be used in an optimization problem..

[Jan]

@Bas: Then you use the first element of venu_name as index of the same variable? Strange!