MATLAB: Why filtering gives nan values.

Question

Am applying low pass filter to my signal data using

 [b11,a11] = butter(5,4/24);
  MM1= filtfilt(b11,a11,MM1);

but the result comes out nan. I don't have any nans in my MM1 data . Any help?

Answer 1

hi,

I think the input has a NaN, look at this example :

 r=rand(100,1);
 [b11,a11] = butter(5,4/24);
 MM1= filtfilt(b11,a11,r); % Normal Filtering
r(end/2)=NaN;    %  FOR example a middle value to be NaN
MM2= filtfilt(b11,a11,r);

MM2 is vector of NaNs, only one NaN value in r produces NaNs in the output .

try :

 isnan(MM1)