Suggestion for rewrite of the for loop and while loop

Hi, i have created a code. However, it takes very long execution time to execute the code.Can anyone suggest a better solution to improve on the code?Here is the code.

%To receive received=fgetl(s); %Get from serial port using fgetl

file=[file received]; %The received bits is joined together to form a stream of bits.

%To form back the file

size_byte=fix(size(file)/32);

   M=size_byte(2);
        Video=[];
         for j=1:M               %For loop to get the binary bits back to matrices format
             b=16*(j);
             a=-15+b;
             Video= [Video;file(a:b)];
         end
              dec=bin2dec(Video);
              fid1=fopen (Save_file, 'wb');
              count=fwrite(fid1, dec, 'uint16');
I have run using the profiler and it stated is the fgetl and Video= [Video;file(a:b)];which cause alot of execution time.Can anyone help to suggest for a better solution?I need it urgently. Thanks.

[Jason Ross]

What is "a long execution time"

How much data are you dealing with?

[Jason Ross]

Do you know how long you think it should take?

Do you have a performance limit you are required to meet?

[MrPuzzled Marc]

I m just dealing with 100kB data yet i needs around 15 mins to send and receive, Could you have any better suggestion?

Answer 1

[Matt Fig]

The major improvement will come from Pre-allocating memory for Video instead of growing the data in the loop. Calculate the final size before the loop and use the ZEROS function to grab the memory before the loop.

[MrPuzzled Marc]

Can you give me an example on how to write the command??

I m blur on preallocation of memory.

Yes, is because of that.

[Matt Fig]

Look at the difference in execution speed!

tic

y = [];

for ii = 1:100000

y = [y,sin(ii)];

end

toc

tic

z = zeros(1,100000); % Pre-allocate memory.

for jj = 1:100000

z(jj) = sin(jj);

end

toc

[Oleg Komarov]

I also gave you a clear example in the other your thread. Check it out.

[Matt Fig]

What do you mean describe more? Did you run the example above? It does the same thing twice, once with pre-allocation and once without. What more do you need to know? Please be specific.

[Matt Fig]

Deleted comment after Oleg's:

MrPuzzled Marc: Can you describe more about pre-allocation?