Add a useful package (from Source forge) for octave

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

diff --git a/octave_packages/signal-1.1.3/zerocrossing.m b/octave_packages/signal-1.1.3/zerocrossing.m
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+## Copyright (C) 2008 Carlo de Falco <carlo.defalco@gmail.com>
+##
+## 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} {@var{x0}} = zerocrossing (@var{x}, @
+## @var{y})
+## Estimates the points at which a given waveform y=y(x) crosses the
+## x-axis using linear interpolation.
+## @seealso{fzero, roots}
+## @end deftypefn
+
+function  retval  = zerocrossing (x,y)
+
+  x = x(:);y = y(:);
+  crossing_intervals = (y(1:end-1).*y(2:end) <= 0);
+  left_ends = (x(1:end-1))(crossing_intervals);
+  right_ends = (x(2:end))(crossing_intervals);
+  left_vals = (y(1:end-1))(crossing_intervals);
+  right_vals = (y(2:end))(crossing_intervals);
+  mid_points = (left_ends+right_ends)/2;
+  zero_intervals = find(left_vals==right_vals);
+  retval1 = mid_points(zero_intervals);
+  left_ends(zero_intervals) = [];
+  right_ends(zero_intervals) = [];
+  left_vals(zero_intervals) = [];
+  right_vals(zero_intervals) = [];
+  retval2=left_ends-(right_ends-left_ends).*left_vals./(right_vals-left_vals);
+  retval = union(retval1,retval2);
+
+endfunction
+
+%!test
+%! x = linspace(0,1,100);
+%! y = rand(1,100)-0.5;
+%! x0= zerocrossing(x,y);
+%! y0 = interp1(x,y,x0);
+%! assert(norm(y0,inf), 0, 100*eps)
+
+%!test
+%! x = linspace(0,1,100);
+%! y = rand(1,100)-0.5;
+%! y(10:20) = 0;
+%! x0= zerocrossing(x,y);
+%! y0 = interp1(x,y,x0);
+%! assert(norm(y0,inf), 0, 100*eps)
+
+%!demo
+%! x = linspace(0,1,100);
+%! y = rand(1,100)-0.5;
+%! x0= zerocrossing(x,y);
+%! y0 = interp1(x,y,x0);
+%! plot(x,y,x0,y0,'x')
+
+%!demo
+%! x = linspace(0,1,100);
+%! y = rand(1,100)-0.5;
+%! y(10:20) = 0;
+%! x0= zerocrossing(x,y);
+%! y0 = interp1(x,y,x0);
+%! plot(x,y,x0,y0,'x')