# HG changeset patch
# User Francesco Potortì <pot@gnu.org>
# Date 1231754085 -3600
# Node ID 1d237a82e3932aa51cf423729c18e07f39867041
# Parent  059fadc0cbc3d1874f10989a1fd5b23cb22ad52b
Add explanation on what wisdom is.

diff --git a/doc/ChangeLog b/doc/ChangeLog
--- a/doc/ChangeLog
+++ b/doc/ChangeLog
@@ -1,3 +1,8 @@
+2008-12-26  Francesco Potortì  <pot@gnu.org>
+
+       * interpreter/signal.txi (Signal Processing): Add explanation of
+       what wisdom is.
+
 2008-08-28  John W. Eaton  <jwe@octave.org>
 
 	* interpreter/plot.txi: Doc fixes suggested by Francesco Potorti`
diff --git a/doc/interpreter/signal.txi b/doc/interpreter/signal.txi
--- a/doc/interpreter/signal.txi
+++ b/doc/interpreter/signal.txi
@@ -23,6 +23,18 @@
 
 @DOCSTRING(fft)
 
+Octave uses the FFTW libraries to perform FFT computations. When Octave
+starts up and initializes the FFTW libraries, they read a system wide
+file (on a Unix system, it is typically @file{/etc/fftw/wisdom}) that
+contains information useful to speed up FFT computations.  This
+information is called the @emph{wisdom}.  The system-wide file allows
+wisdom to be shared between all applications using the FFTW libraries.
+
+Use the @code{fftw} function to generate and save wisdom.  Using the
+utilities provided together with the FFTW libraries
+(@command{fftw-wisdom} on Unix systems), you can even add wisdom
+generated by Octave to the system-wide wisdom file.
+
 @DOCSTRING(fftw)
 
 @DOCSTRING(ifft)