Add a useful package (from Source forge) for octave

[CreaPhase.git] / octave_packages / signal-1.1.3 / fht.m

diff --git a/octave_packages/signal-1.1.3/fht.m b/octave_packages/signal-1.1.3/fht.m
new file mode 100644 (file)
index 0000000..2a85f09
--- /dev/null
+++ b/octave_packages/signal-1.1.3/fht.m
@@ -0,0 +1,69 @@
+## Copyright (C) 2008 Muthiah Annamalai <muthiah.annamalai@uta.edu>
+## 
+## This program is free software; you can redistribute it and/or modify it under
+## the terms of the GNU General Public License as published by the Free Software
+## Foundation; either version 3 of the License, or (at your option) any later
+## version.
+##
+## This program is distributed in the hope that it will be useful, but WITHOUT
+## ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+## FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
+## details.
+##
+## You should have received a copy of the GNU General Public License along with
+## this program; if not, see <http://www.gnu.org/licenses/>.
+
+## -*- texinfo -*-
+## @deftypefn{Function File} {m = } fht ( d, n, dim )
+## @cindex linear algebra 
+##  The function fht calculates  Fast Hartley Transform
+##  where @var{d} is the real input vector (matrix), and @var{m}
+## is the real-transform vector. For matrices the hartley transform
+## is calculated along the columns by default. The options
+## @var{n},and @var{dim} are similar to the options of FFT function.
+## 
+## The forward and inverse hartley transforms are the same (except for a
+## scale factor of 1/N for the inverse hartley transform), but
+## implemented using different functions .
+##
+## The definition of the forward hartley transform for vector d,
+## @math{
+## m[K] = \sum_{i=0}^{N-1} d[i]*(cos[K*2*pi*i/N] + sin[K*2*pi*i/N]), for  0 <= K < N.
+## m[K] = \sum_{i=0}^{N-1} d[i]*CAS[K*i], for  0 <= K < N. }
+## 
+## @example
+## fht(1:4)
+## @end example
+## @seealso{ifht,fft}
+## @end deftypefn
+
+function m = fht( d, n, dim )
+  
+  if ( nargin < 1 )
+    print_usage();
+  end
+
+  if ( nargin == 3 )
+    Y = fft(d,n,dim);
+  elseif ( nargin == 2 )
+    Y = fft(d,n);
+  else 
+    Y = fft(d);
+  end
+  
+  m = real(Y) - imag(Y);
+
+#   -- Traditional --
+#   N = length(d);
+#   for K = 1:N
+#     i = 0:N-1;
+#     t = 2*pi*(K-1).*i/N;
+#     ker = (cos(t) + sin(t));
+#     val = dot(d,ker);
+#     m(K) = val;
+#   end
+
+end
+%!
+%!assert( fht([1 2 3 4]),[10 -4 -2 0] )
+%!