lfilter_c

rewrite python scipy.signal.lfilter in c code

src https://github.com/scipy/scipy/blob/master/scipy/signal/lfilter.c.src

c code

float b[3] = { 0.00013651, 0.00027302, 0.00013651 };
float a[3] = { 1., -1.96668139 , 0.96722743 };
float x[10] = { 2,5,6,7,8,2,3,5,1,2 };
float delay[2] = { 0 ,0 };
float y[1] = {};
for (int i = 0; i < 10; i++)
{
  bb_digital_float_filter(b, a, &x[i], y, delay, 3, 1, 1, 1);
  printf("%f\n", y[0]);
}

output: 0.000273 0.001766 0.005665 0.012711 0.023340 0.037021 0.052282 0.068788 0.086627 0.105062

In python code

from scipy.signal import butter, sosfilt, lfilter
import numpy as np

breath_sos = np.concatenate(butter(2, 0.0075))  #here is the example of b coefficient and a coefficient from python code
breath_zi = np.zeros((1, 2))

testlist = [2,5,6,7,8,2,3,5,1,2]

for i in testlist:
    y_breath, breath_zi = sosfilt(breath_sos, np.array([i]), zi=breath_zi)
    print(y_breath)

output: [0.00027302] [0.00176554] [0.00566538] [0.01271057] [0.02334023] [0.03702156] [0.05228196] [0.06878833] [0.08662732] [0.10506299]