def _butter_analog_poles(n):
 poles = []
 for k in range(((- n) + 1), n, 2):
  poles.append((- mpmath.exp((((1j * mpmath.pi) * k) / (2 * n)))))
 return poles

def _butter_analog_poles ( n ) : poles = [ ] for k in range ( ( ( - n ) + 1 ) , n , 2 ) : poles . append ( ( - mpmath . exp ( ( ( ( 1j * mpmath . pi ) * k ) / ( 2 * n ) ) ) ) ) return poles
poles of an analog butterworth lowpass filter .