Add a useful package (from Source forge) for octave

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

diff --git a/octave_packages/signal-1.1.3/downsample.m b/octave_packages/signal-1.1.3/downsample.m
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+## Author: Paul Kienzle <pkienzle@users.sf.net> (2007)
+## This program is granted to the public domain.
+
+## -*- texinfo -*-
+## @deftypefn {Function File} {@var{y} =} downsample (@var{x}, @var{n})
+## @deftypefnx {Function File} {@var{y} =} downsample (@var{x}, @var{n}, @var{offset})
+## Downsample the signal, selecting every nth element.  If @var{x}
+## is a matrix, downsample every column.
+##
+## For most signals you will want to use @code{decimate} instead since
+## it prefilters the high frequency components of the signal and
+## avoids aliasing effects.
+##
+## If @var{offset} is defined, select every nth element starting at
+## sample @var{offset}.
+## @seealso{decimate, interp, resample, upfirdn, upsample}
+## @end deftypefn
+
+function y = downsample (x, n, phase = 0)
+
+  if nargin<2 || nargin>3, print_usage; end
+
+  if phase > n - 1
+    warning("This is incompatible with Matlab (phase = 0:n-1). See ...
+    octave-forge signal package release notes for details.")
+  end
+
+  if isvector(x)
+    y = x(phase + 1:n:end);
+  else
+    y = x(phase + 1:n:end,:);
+  end
+endfunction
+
+%!assert(downsample([1,2,3,4,5],2),[1,3,5]);
+%!assert(downsample([1;2;3;4;5],2),[1;3;5]);
+%!assert(downsample([1,2;3,4;5,6;7,8;9,10],2),[1,2;5,6;9,10]);
+%!assert(downsample([1,2,3,4,5],2,1),[2,4]);
+%!assert(downsample([1,2;3,4;5,6;7,8;9,10],2,1),[3,4;7,8]);