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Mark Borgerding 2003-10-10 02:04:59 +00:00
parent 18e5e8e360
commit 66b0646c9c
1 changed files with 11 additions and 6 deletions
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17
fft.py
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@ -4,21 +4,18 @@ pi=math.pi
e=math.e e=math.e
j=complex(0,1) j=complex(0,1)
def T(n,k):
return e ** -2*j*pi*k/n
def fft(f): def fft(f):
n=len(f) n=len(f)
if n==1: if n==1:
return f return f
for p in 4,3,2,5: for p in 2,3,5:
if n%p==0: if n%p==0:
break break
else: else:
raise Exception('%s not factorable ' % n) raise Exception('%s not factorable ' % n)
m = n/p
m = n/p
Fm=[] Fm=[]
for q in range(p): # 0,1 for q in range(p): # 0,1
fp = f[q::p] fp = f[q::p]
@ -29,9 +26,17 @@ def fft(f):
for k in range(n): for k in range(n):
val = 0 val = 0
for q in range(p): for q in range(p):
t = e ** ( -j*2*pi*k*q/n ) t = e ** ( j*2*pi*k*q/n )
val += Fm[ q*m + (k%m) ] * t val += Fm[ q*m + (k%m) ] * t
Fout[k] = val Fout[k] = val
return Fout return Fout
def test(f=range(256),ntimes=10):
import time
t0 = time.time()
for i in range(ntimes):
fft(f)
t1 = time.time()
print '%ss'% (t1-t0)