1 files changed, 67 insertions, 0 deletions
diff --git a/numpy/dft/helper.py b/numpy/dft/helper.py
new file mode 100644
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+++ b/numpy/dft/helper.py
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+"""
+Discrete Fourier Transforms - helper.py
+"""
+# Created by Pearu Peterson, September 2002
+
+__all__ = ['fftshift','ifftshift','fftfreq']
+
+from scipy.base import asarray, concatenate, arange, take, \
+		array, integer
+import types
+
+def fftshift(x,axes=None):
+    """ fftshift(x, axes=None) -> y
+
+    Shift zero-frequency component to center of spectrum.
+
+    This function swaps half-spaces for all axes listed (defaults to all).
+
+    Notes:
+      If len(x) is even then the Nyquist component is y[0].
+    """
+    tmp = asarray(x)
+    ndim = len(tmp.shape)
+    if axes is None:
+        axes = range(ndim)
+    y = tmp
+    for k in axes:
+        n = tmp.shape[k]
+        p2 = (n+1)/2
+        mylist = concatenate((arange(p2,n),arange(p2)))
+        y = take(y,mylist,k)
+    return y
+
+
+def ifftshift(x,axes=None):
+    """ ifftshift(x,axes=None) - > y
+
+    Inverse of fftshift.
+    """
+    tmp = asarray(x)
+    ndim = len(tmp.shape)
+    if axes is None:
+        axes = range(ndim)
+    y = tmp
+    for k in axes:
+        n = tmp.shape[k]
+        p2 = n-(n+1)/2
+        mylist = concatenate((arange(p2,n),arange(p2)))
+        y = take(y,mylist,k)
+    return y
+
+def fftfreq(n,d=1.0):
+    """ fftfreq(n, d=1.0) -> f
+
+    DFT sample frequencies
+
+    The returned float array contains the frequency bins in
+    cycles/unit (with zero at the start) given a window length n and a
+    sample spacing d:
+
+      f = [0,1,...,n/2-1,-n/2,...,-1]/(d*n)         if n is even
+      f = [0,1,...,(n-1)/2,-(n-1)/2,...,-1]/(d*n)   if n is odd
+    """
+    assert isinstance(n,types.IntType) or isinstance(n, integer)
+    k = range(0,(n-1)/2+1)+range(-(n/2),0)
+    return array(k,'d')/(n*d)
+