fprintf

[hoopz]

I'm trying to write all of the data in a matrix into a file, and I have to have a header in this file so I'm using fprintf instead of dlmwrite or something like that.

I have a matrix A, and the format I want the file to be in is:

<header>
A(1,1) A(1,2) A(1,3)
A(2,1) A(2,2) A(2,3)
etc, etc.

After I write the header, I could put A in the file by using the command:

fprintf(file, '%g %g %g\n',A);


The problem is, A is actually 707 columns wide and 353 rows long, so it's impractical for me to write '%g' 707 times. How can I do this?


Thanks

 

[brokensoul]

You can use this, dlmwrite(filename, M, '-append').
This way you can write your header with a seperate function and then you dlmwrite to drop the whole matrix in underneath it.

you can read more here

Hope this helps.
BsK

 

[hoopz]

Thanks BsK, you are awesome. I should have realized you could use dlmwrite even if you had some text, it just seem kinda funny to me that I had to pound everything out with fprintf.

 

[hoopz]

As a follow up to this I've decided to stick with fprintf. I used a 'for' loop to create a string that is 707 identifiers long, e.g. '%.16g %.16g %.16g etc. etc.'. My program took 11 seconds to run when using fprintf.

I figured using dlmwrite and '-append' would have been faster, but it turned out to be about the same speed and then I realized I hadn't specified precision. When I put 'precision','%.16g' in to my dlmwrite command, the program took 130 seconds to complete! More than ten times what it did with fprintf.

I would have thought dlmwrite would have been faster, but I'm sticking with fprintf even if it looks kinda ugly.

 

[brokensoul]

Hoopz
just curious..

What was your delimiter with dlmwrite?


How long did it take for the script to write out the identifiers?


BsK

 

[hoopz]

The format I needed to put the data in was space-delimited, so my delimiter with dlmwrite was simply a ' '

I just used the code below to create the identifer string; there is probably a better way to do it. Still, Matlab reported the elapsed time as only 0.122 seconds, although I am on a speedy comp - 3.8 GHz P4, with 2 GB of RAM.

a = '%.16g';
for i=1:706
a= [a ' %.16g'];
end
a = [a '\n'];

 

[MikeyP]

How about this

A = rand(707,353);
a = '%.16g '; 
b = repmat(a,1,353);
b = [b '\n'];

f = fopen('test.txt','w');
fprintf(f,'%s\n', 'My header information');
fprintf(f, b, A.');

fclose(f);

M

--
Dr Michael F Platten