Add the interpolation function (required for all the 1D simulations)

diff --git a/utilities_ESRF/interp.m b/utilities_ESRF/interp.m
new file mode 100644 (file)
index 0000000..d129783
--- /dev/null
+++ b/utilities_ESRF/interp.m
@@ -0,0 +1,58 @@
+## 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.