[Scipy-svn] r5468 - trunk/scipy/fftpack

[scipy-svn at scipy.org]

Author: cdavid
Date: 2009-01-16 01:34:25 -0600 (Fri, 16 Jan 2009)
New Revision: 5468

Modified:
   trunk/scipy/fftpack/realtransforms.py
Log:
Add definition of dct II we use, + refs.

Modified: trunk/scipy/fftpack/realtransforms.py
===================================================================
--- trunk/scipy/fftpack/realtransforms.py	2009-01-16 07:34:10 UTC (rev 5467)
+++ trunk/scipy/fftpack/realtransforms.py	2009-01-16 07:34:25 UTC (rev 5468)
@@ -31,7 +31,14 @@
 def dct2(x, n=None):
     """
     Return Discrete Cosine Transform (type II) of arbitrary type sequence x.
+    There are several definitions, we use the following:
 
+                  N-1
+        y[k] = 2* sum x[n]*cos(pi*k*(2n+1)/(2*N)), 0 <= k < N.
+                  n=0
+
+    In particular, we do not normalize it by the number of points of the DCT N.
+
     Parameters
     ----------
     x : array-like
@@ -42,6 +49,14 @@
     Returns
     -------
     y : real ndarray
+
+    References
+    ----------
+
+    http://en.wikipedia.org/wiki/Discrete_cosine_transform
+
+    'A Fast Cosine Transform in One and Two Dimensions', by J. Makhoul, in IEEE
+    Transactions on acoustics, speech and signal processing.
     """
     return _dct(x, 2, n)