Avoid str2double and str2num. Use sscanf instead.

For scalars, you’ll see a modest improvement.

>> str = '0009';
>> tic; for p=1:1000, str2num(str); end; toc
Elapsed time is 0.126388 seconds.
>> tic; for p=1:1000, sscanf(str, '%d'); end; toc
Elapsed time is 0.022299 seconds.

>> str = '3.14159265';
>> tic; for p=1:1000, str2double(str); end; toc
Elapsed time is 0.056466 seconds.
>> tic; for p=1:1000, sscanf(str, '%f'); end; toc
Elapsed time is 0.017805 seconds.

For vectors, you’ll see a more hefty speed up.

>> str = '0009 3.14159265';
>> tic; for p=1:1000, str2double(str); end; toc
Elapsed time is 0.480512 seconds.
>> tic; for p=1:1000, sscanf(str, '%f'); end; toc
Elapsed time is 0.027449 seconds.

Also favor sprintf instead of num2str.

>> tic; for p=1:1000, num2str(p); end; toc
Elapsed time is 0.101599 seconds.
>> tic; for p=1:1000, sprintf('%d', p); end; toc
Elapsed time is 0.018325 seconds.