Butterworth filter design calls bilinear and fails

I am attempting to set up a simple low-pass Butterworth filter using the following line of code:

[b,a]=butter(2,1/8,'low');

This produces the following error(s):

Error using bilinear

Too many output arguments.

Error in butter>butterImpl (line 130)

[ad,bd,cd,dd] = bilinear(ad,bd,cd,dd,fs);

Error in butter (line 59)

[varargout{1:nargout}] = butterImpl(n,Wn,varargin{:});

As far as I can tell, this is a valid call of bilinear (i.e. five inputs, four outputs). Can anyone replicate this problem? I'm using R2020b Update 3 with the signal processing toolbox. I haven't changed the butter function at all.

[Mathieu NOE]

hi

it works on my R2020b Update 1

>> [b,a]=butter(2,1/8,'low');

>> b

b =

0.0300 0.0599 0.0300

>> a

a =

1.0000 -1.4542 0.5741

[Sam Kastner]

After a full reinstall, this doesn't seem to be an issue any more.

[Shiyu]

I got the same issue in my university's cluster, I double check the "bilinear.m" and "butter.m" function, both in toolbox/signal/signal/

University Clutser MATLAB Version is R2024a

I also run MATLAB R2024a on my local device

Local device is completely fine, but university cluster always goes wrong!

I double check the two functions in my local and uni cluster, the bilinear.m is completely the same

while the 'butter.m' is different

Answer 1

[Adam Danz]

You likely had another file on your Matlab path with the same name as butter. If the error happens again, the following command will show all functions and files of that name and will indicate which one you're using. Remove the path(s) to the functions that don't point to Matlab's butter() or rename the custom files/functions.

which butter -all

should point to \toolbox\signal\signal\butter.m (in r2020b).

[Sam Kastner]

Yes, serves me right for blindly adding a folder of third party functions to my path. Thanks!