X-Git-Url: https://git.creatis.insa-lyon.fr/pubgit/?p=CreaPhase.git;a=blobdiff_plain;f=octave_packages%2Fsignal-1.1.3%2Fifht.m;fp=octave_packages%2Fsignal-1.1.3%2Fifht.m;h=67b3518f6f9c765e86f378f08ec1407d4e2251bf;hp=0000000000000000000000000000000000000000;hb=f5f7a74bd8a4900f0b797da6783be80e11a68d86;hpb=1705066eceaaea976f010f669ce8e972f3734b05

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+## 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 = } ifht ( d, n, dim )
+## @cindex linear algebra 
+##  The function ifht 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] = 1/N \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] = 1/N \sum_{i=0}^{N-1} d[i]*CAS[K*i], for  0 <= K < N. }
+## 
+## @example
+## ifht(1:4)
+## @end example
+## @seealso{fht,fft}
+## @end deftypefn
+
+function m = ifht( d, n, dim )
+
+  if ( nargin < 1 )
+    print_usage();
+  end
+
+  if ( nargin == 3 )
+    Y = ifft(d,n,dim);
+  elseif ( nargin == 2 )
+    Y = ifft(d,n);
+  else
+    Y = ifft(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)./N;
+#     m(K) = val;
+#   end
+
+end
+
+%!assert(ifht(fht(1:4)),[1 2 3 4])