fir: cleanup halfgen4

This commit is contained in:
Robert Jördens 2016-12-17 21:19:46 +01:00
parent 5f3033b518
commit f310274e39
1 changed files with 10 additions and 6 deletions

View File

@ -1,11 +1,10 @@
from operator import add
from functools import reduce
from collections import namedtuple
import numpy as np
from migen import *
def halfgen4(width, n):
def halfgen4(width, n, df=1e-3):
"""
http://recycle.lbl.gov/~ldoolitt/halfband
@ -24,13 +23,18 @@ def halfgen4(width, n):
target = .5*np.ones_like(wfit)
basis = np.cos(wfit*np.arange(1, 2*n, 2))
l = np.linalg.pinv(basis)@target
weight = np.ones_like(wfit)
f0 = None
for i in range(40):
err = np.fabs(basis@l - .5)
weight[err > .99*np.max(err)] *= 1 + 1.5/(i + 11)
l = np.linalg.pinv(basis*weight)@(target*weight)
err = np.fabs(basis@l - .5)
f = np.max(err)/np.mean(err)
if f0 and (f0 - f)/(f0 + f) < df/2:
break
f0 = f
weight[err > (1 - df)*np.max(err)] *= 1 + 1.5/(i + 11)
a = np.c_[l, np.zeros_like(l)].ravel()[:-1]
a = np.r_[a[::-1], 1, a]/2
return a