/usr/share/octave/packages/signal-1.2.2/interp.m is in octave-signal 1.2.2-1build1.
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 | ## Copyright (C) 2000 Paul Kienzle <pkienzle@users.sf.net>
##
## 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/>.
## usage: y = interp(x, q [, n [, Wc]])
##
## Upsample the signal x by a factor of q, using an order 2*q*n+1 FIR
## filter. Note that q must be an integer for this rate change method.
## n defaults to 4 and Wc defaults to 0.5.
##
## Example
## # Generate a signal.
## t=0:0.01:2; x=chirp(t,2,.5,10,'quadratic')+sin(2*pi*t*0.4);
## y = interp(x(1:4:length(x)),4,4,1); # interpolate a sub-sample
## stem(t(1:121)*1000,x(1:121),"-g;Original;"); hold on;
## stem(t(1:121)*1000,y(1:121),"-r;Interpolated;");
## stem(t(1:4:121)*1000,x(1:4:121),"-b;Subsampled;"); hold off;
##
## See also: decimate, resample
function y = interp(x, q, n = 4, Wc = 0.5)
if nargin < 1 || nargin > 4,
print_usage;
endif
if q != fix(q), error("decimate only works with integer q."); endif
if rows(x)>1
y = zeros(length(x)*q+q*n+1,1);
else
y = zeros(1,length(x)*q+q*n+1);
endif
y(1:q:length(x)*q) = x;
b = fir1(2*q*n+1, Wc/q);
y=q*fftfilt(b, y);
y(1:q*n+1) = []; # adjust for zero filter delay
endfunction
%!demo
%! ## Generate a signal.
%! t=0:0.01:2; x=chirp(t,2,.5,10,'quadratic')+sin(2*pi*t*0.4);
%! y = interp(x(1:4:length(x)),4,4,1); # interpolate a sub-sample
%! plot(t(1:121)*1000,y(1:121),"r-+;Interpolated;"); hold on;
%! stem(t(1:4:121)*1000,x(1:4:121),"ob;Original;"); hold off;
%!
%! % graph shows interpolated signal following through the
%! % sample points of the original signal.
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