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works on Fout in-place

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This commit is contained in:
Mark Borgerding 2003-10-10 21:30:18 +00:00
parent edf93e8540
commit 08be1d86b4
1 changed files with 5 additions and 8 deletions
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13
fft.py
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@ -16,23 +16,20 @@ def fft(f):
raise Exception('%s not factorable ' % n) raise Exception('%s not factorable ' % n)
m = n/p m = n/p
Fm=[] Fout=[]
for q in range(p): # 0,1 for q in range(p): # 0,1
fp = f[q::p] fp = f[q::p]
Fp = fft( fp ) Fp = fft( fp )
Fm.extend( Fp ) Fout.extend( Fp )
Fout = [ 0 ] * n
for u in range(m): for u in range(m):
scratch = Fm[u::m] # u to end in strides of m scratch = Fout[u::m] # u to end in strides of m
for q1 in range(p): for q1 in range(p):
k = q1*m + u # indices to Fout above that became scratch k = q1*m + u # indices to Fout above that became scratch
val = Fm[ u ] Fout[ k ] = scratch[0]
for q in range(1,p): for q in range(1,p):
t = e ** ( j*2*pi*k*q/n ) t = e ** ( j*2*pi*k*q/n )
#Fout[ k ] += scratch[q] * t Fout[ k ] += scratch[q] * t
val += Fm[ q*m + u ] * t
Fout[ k ] = val
return Fout return Fout