From: uche on 30 Jan 2010 13:33 Hi, I have the following FFT python code and it doesn't seem to compile correctly. To run it, please create a file called output.csv with 1,2,3,4,5,6,7,8. simply run the main function. I get an error such as the following: x[a], x[b] = x[(a)] + W[(n % N)] * x[(b)], x[(a)]  W[(n % N)] * x [(b)] TypeError: list indices must be integers, not float How can I fixe this problem ? I have tried puttin int on all of the variables, but I don't think that is the intension of the person who wore the original code. #!/usr/bin/python """ FFT using CooleyTukey algorithm where N = 2^n. The choice of e^{j2\pi/N} or e^{j2\pi/N} is made by 'sign=1' or 'sign=1' respectively. Since I prefer Engineering convention, I chose 'sign=1' as the default. FFT is performed as follows: 1. bitreverse the array. 2. partition the data into group of m = 2, 4, 8, ..., N data points. 3. for each group with m data points, 1. divide into upper half (section A) and lower half (section B), each containing m/2 data points. 2. divide unit circle by m. 3. apply "butterfly" operation a = 1 wa or a, b = a+w*b, aw*b b 1 wb where a and b are data points of section A and B starting from the top of each section, and w is data points along the unit circle starting from z = 1+0j. FFT ends after applying "butterfly" operation on the entire data array as whole, when m = N. """ def main(): array = [] array2 = [] import os import time os.path.exists("input.csv") fin=open('input.csv', 'r') for line in fin: #read the line from the file array=line.split(',') for a in range(len(array)): #convert into integers array2.append((array[a])) Ti=time.time() print (fft(array2)) Tf=time.time() print (("It took"),TfTi,("seconds to calculate an FFT of size"),len(array)) #end timer """ Find 2^n that is equal to or greater than. """ def nextpow2(i): n = 2 while n < i: n = n * 2 return n """ Return bitreversed list, whose length is assumed to be 2^n: eg. 0111 <> 1110 for N=2^4. """ def bitrev(x): N, x = len(x), x[:] if N != nextpow2(N): raise ValueError ('N is not power of 2') for i in range(N): k, b, a = 0, N>>1, 1 while b >= a: if b & i: k = k  a if a & i: k = k  b b, a = b>>1, a<<1 if i < k: x[i], x[k] = (x[k],x[i]) return x def fft(x, sign=1): from cmath import pi, exp N, W = len(x), [] for i in range(N): # exp(j...) is default W.append(exp(sign * 2j * pi * i / N)) x = bitrev(x) m = 2 while m <= N: for s in range(0,N,m): for i in range (int(m/2)): n = i * N / m a, b = s + i, s + i + m/2 x[a], x[b] = x[(a)] + W[(n % N)] * x[(b)], x[(a)]  W [(n % N)] * x[(b)] m = m * 2 return x
From: Stefan Behnel on 30 Jan 2010 13:52 uche, 30.01.2010 19:33: > I have the following FFT python code You didn't seriously implement an FFT in plain Python code, did you? FFTs are amongst the first thing that come to my mind when I try to imagine what I'd use NumPy for. (and I *never* used it!) Stefan
From: MRAB on 30 Jan 2010 14:08 uche wrote: > Hi, > I have the following FFT python code and it doesn't seem to compile > correctly. To run it, please create a file called output.csv with > 1,2,3,4,5,6,7,8. simply run the main function. I get an error such as > the following: > > x[a], x[b] = x[(a)] + W[(n % N)] * x[(b)], x[(a)]  W[(n % N)] * x > [(b)] > TypeError: list indices must be integers, not float > > How can I fixe this problem ? I have tried puttin int on all of the > variables, but I don't think that is the intension of the person who > wore the original code. > Which version of Python are you using? In Python 3 the division operator '/' returns a float, whereas in Python 2 it returns an int if both operands are int. In Python 3 the int division operator is '//', which is also accepted in recent versions of Python 2. [snip] > > os.path.exists("input.csv") > > fin=open('input.csv', 'r') > > for line in fin: #read the line from the file > > array=line.split(',') > These lines should be indented more: > for a in range(len(array)): #convert into integers > > array2.append((array[a])) > array2.append(int(array[a])) [snip]
From: uche on 30 Jan 2010 14:18 On Jan 30, 2:08 pm, MRAB <pyt...(a)mrabarnett.plus.com> wrote: > uche wrote: > > Hi, > > I have the following FFT python code and it doesn't seem to compile > > correctly. To run it, please create a file called output.csv with > > 1,2,3,4,5,6,7,8. simply run the main function. I get an error such as > > the following: > > > x[a], x[b] = x[(a)] + W[(n % N)] * x[(b)], x[(a)]  W[(n % N)] * x > > [(b)] > > TypeError: list indices must be integers, not float > > > How can I fixe this problem ? I have tried puttin int on all of the > > variables, but I don't think that is the intension of the person who > > wore the original code. > > Which version of Python are you using? In Python 3 the division operator > '/' returns a float, whereas in Python 2 it returns an int if both > operands are int. In Python 3 the int division operator is '//', which > is also accepted in recent versions of Python 2. > > [snip] > > > os.path.exists("input.csv") > > > fin=open('input.csv', 'r') > > > for line in fin: #read the line from the file > > > array=line.split(',') > > These lines should be indented more: > > > for a in range(len(array)): #convert into integers > > > array2.append((array[a])) > > array2.append(int(array[a])) > > [snip] Thanks, I just got this code from a site and trying to compile it. it's just a nightmare! I got another problem after changing / to // . Yes, I am using 3.1. W.append(exp(sign * 2j * pi * i // N)) TypeError: can't take floor of complex number.
From: Stefan Behnel on 30 Jan 2010 14:21 Stefan Behnel, 30.01.2010 19:52: > uche, 30.01.2010 19:33: >> I have the following FFT python code > > You didn't seriously implement an FFT in plain Python code, did you? Sorry, no, you didn't. Should have read your post a little closer. > FFTs > are amongst the first thing that come to my mind when I try to imagine what > I'd use NumPy for. (and I *never* used it!) On second thought, I'd probably use FFTW for that, and there seem to be Python bindings for it: http://developer.berlios.de/projects/pyfftw/ Stefan

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