Getting the error “ `butter' undefined” in Octave. How to fix it?

Question

When I write this line in Octave:

[b,a] = butter (5,0.2);

I get the error:

error: `butter' undefined near line 1 column 10

How can I get rid of it? Thanks.

Answer 1

Seems that you forgot to load the signal package. You have to install and load it in order to use the butter function:

pkg install -forge signal
pkg load signal
[b,a] = butter (5,0.2);

Please take a look in the Octave documentation . It explains how to install and how to load packages.

Answer 2

The butter function is part of the signal package. You need to download, install and load the package before you can use its functions:

>> pkg install -forge signal
>> pkg load signal