Error in calling a function and writing to file

I'm trying to call a function out of a script, it's a simple one as we've just started, but I keep getting an error on my fprintf line. Theoretically its supposed to work through different files where one is the function and one is the script whilst both are in the same directory.

This is the function:

function [out]=summation(N)

S=0;
for k=1:N
    S=S+(1/k^2);
end

out=S;

end

This is the script

fid = fopen('summationfile.txt', 'w');

for i=1:50
    sumvalue=summation(i);
    fprintf(fid,'N= %.0f \t S= %.4f \r\n',i,sumvalue);
end

fclose(fid)

Initially I was getting an error about just one line but figured its because the files are separate and if I can get them to work locally moving them to different files wont be as difficult so at the moment they are in the same file and this is the error I receive.

Error using fprintf
Invalid file identifier. Use fopen to generate a valid file identifier.

Error in summationfile (line 5)
    fprintf(fid,'N= %.0f \t S= %.4f \r\n',i,sumvalue);

Answer 1

[Walter Roberson]

Change

fid = fopen('summationfile.txt', 'w');

to

filename = 'summationfile.txt';
[fid, msg] = fopen(filename, 'w');
if fid < 0
  error('Failed to open file "%s" because "%s"', filename, msg);
end

[Mitul Dattani]

Fixed my initial problem now i get this:

Failed to open file "summationfile.txt" because "Permission denied"

[Walter Roberson]

You do not have permission to write a file with that name in that location.

In particular, Windows does not permit you to write files under the Programs and Executables directory, so if you are currently cd'd to the directory that MATLAB is installed in, you will not be able to write files there. In that case you should probably change directories, such as to your Documents\MATLAB directory

[Mitul Dattani]

Yeah it works when i run matlab as admin, how would I go about changing the directory for matlab though so I dont have to run it as admin again? I always assumed when running adding the directory to the path did it for me but obviously thats not the case.

[Walter Roberson]

When you are writing files, MATLAB always assumes that you want to write into your current directory unless you give the path to where you want to write. So the easiest is to use cd to change directories to a directory that you do your MATLAB work in.