Python error when calling Fourier transform code

Question

I have some difficulty in running the code. When I run it, this kind of error always appears:

Traceback (most recent call last):
  File "C:\Users\zhangjq058\workspace\22222222\src\222.py", line 20, in <module>
    x, y = meshgrid(fftfreq(th.shape[0], dx), fftfreq(th.shape[1], dx))
  File "C:\Python27\lib\site-packages\numpy\fft\helper.py", line 153, in fftfreq
    assert isinstance(n,types.IntType) or isinstance(n, integer)
AssertionError

The code is:

from pylab import *
from numpy import *
N = 100 #lattice points per axis
dt = 1 #time step
dx = 1 #lattice spacing
t = arange(0, 10000*dt, dt) #time
a = 1 #cofficient
epsilon = 100 #cofficient
M = 1.0 #cofficient
every = 100 #dump an image every
phi_0 = 0.5 #initial mean value of the order parameter
noise = 0.1 #initial amplitude of thermal fluctuations in the order parameter
th = phi_0*ones((N, N)) + noise*(rand(N, N) - 0.5) #initial condition
x, y = meshgrid(fftfreq(th.shape[0], dx), fftfreq(th.shape[1], dx))
k2 = (x*x + y*y) #k is a victor in the Fourier space, k2=x^2+y^2
g = lambda th, a: 4*a*th*(1-th)*(1-2*th) #function g
def update(th, dt, a, k2): 
    return ifft2((fft2(th)-dt*M*k2*fft2(g(th,a)))/(1+2*epsilon*M*dt*k2**2))

for i in range(size(t)):
    print t[i]
    if mod(i, every)==0:
        imshow(abs(th), vmin=0.0, vmax=1.0)
        colorbar()
        savefig('t'+str(i/every).zfill(3)+'.png', dpi=100)
        clf()
th=update(th, dt, a, k2)

Please edit this post, and re-post the code, selecting it and clicking the {} (code format) button, instead of double-spacing every line. — Jonathon Reinhart
– Jonathon Reinhart, Commented May 21, 2014 at 8:42
Neither can I on Python 2.7.6, Fedora 19; can you share your setup? — Andrey Sobolev
– Andrey Sobolev, Commented May 21, 2014 at 10:03
Hey, mine's Python 2.7. But I use PyDev (Python IDE). I think probably there is something wrong with the IDE. — Porter
– Porter, Commented May 21, 2014 at 10:18
By the way, did you both run the code successfully? Is there any other problem? Thank you! — Porter
– Porter, Commented May 21, 2014 at 10:40

tillsten · Accepted Answer · 2014-05-21 11:57:34Z

2

You are under Windows 64-bit i assume. There is a bug in your numpy version, where windows Long type is not recognized as int. Either update numpy or cast your shapes manually:

fftfreq(int(th.shape[0]), dx)

answered May 21, 2014 at 11:57

tillsten

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Porter Over a year ago

You are right! I modified the code according to your advice. It works! :>. But one is that the code aims at demonstrating the change of th (composition) in 2D real space with time. why couldn't I see the figure while I was running it? Thank you!

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