Octave function reference: butter filter

Jovan Stosic November 3, 2019 
 sf = 800; sf2 = sf/2;
 data=[[1;zeros(sf-1,1)],sinetone(25,sf,1,1),sinetone(50,sf,1,1),sinetone(100,sf,1,1)];
 [b,a]=butter ( 1, 50 / sf2 );
 filtered = filter(b,a,data);

 clf
 subplot ( columns ( filtered ), 1, 1)
 plot(filtered(:,1),";Impulse response;")
 subplot ( columns ( filtered ), 1, 2 )
 plot(filtered(:,2),";25Hz response;")
 subplot ( columns ( filtered ), 1, 3 )
 plot(filtered(:,3),";50Hz response;")
 subplot ( columns ( filtered ), 1, 4 )
 plot(filtered(:,4),";100Hz response;")

Source: Function Reference: butter

SymPy

Jovan Stosic October 26, 2019

SymPy is a Python library for symbolic computation. It provides computer algebra capabilities either as a standalone application, as a library to other applications, or live on the web as SymPy Live or SymPy Gamma. SymPy is simple to install and to inspect because it is written entirely in Python with few dependencies.[2][3][4] This ease of access combined with a simple and extensible code base in a well known language make SymPy a computer algebra system with a relatively low barrier to entry.

SymPy includes features ranging from basic symbolic arithmetic to calculus, algebra, discrete mathematics and quantum physics. It is capable of formatting the result of the computations as LaTeX code.[2][3]

SymPy is free software and is licensed under New BSD License. The lead developers are Ondřej Čertík and Aaron Meurer.

Source: SymPy – Wikipedia