Correct Code for function Butter?

I need filter a data of displacement, and teh data is save in a txt file, this txt has 100 rows and 4 coluns. Until the begin of second for the code is working, but i think de last for doesn´t work. My frequency of acquisition is 210 Hz and my cutoff frequency is 6 Hz, and i need a low pass butterworth filter 4 ordem.

Sorry for my English.

clear all
Files=dir('filter*.txt');
[z,n]=size(Files);
for x=1:z
    arq=load(Files(x).name);
    [v,b]=size(arq);
    for m=1:b
        %4th order, with 6 Hz of cutoff frequency and 210Hz of acquisition
        [a,b]=butter(4,6(210/2),'low');
        exitfile(m,:)=filter(a,b.arq(m,:);
    end
        savefile=['clean','.',Files(x).name];
        save(fullfile('c:','TCC',savefile,'exitfile','-ASCII');
end

[Jan]

The description "I think the last FOR does not work" does not contain enough information to allow for a specific answer. Please explain, why you assume that.

Btw.: The butter() command consumes some time, therefore it is more efficient to move it out of the loops.

[Walter Roberson]

duplicate is at http://www.mathworks.co.uk/matlabcentral/answers/53616-how-i-use-the-command-butter

Answer 1

[Jan]

In the line

[a,b]=butter(4,6(210/2),'low');

the expression "6(210/2)" is no valid Matlab syntax. Do you mean "6 * (210 / 2)"?

[Marcelo Costa]

Jan, try this topic http://www.mathworks.com/matlabcentral/answers/53616-how-i-use-the-command-butter