--- a/main/signal/INDEX	Sat Jul 11 07:30:31 2009 +0000
+++ b/main/signal/INDEX	Sat Jul 11 19:20:27 2009 +0000
@@ -34,6 +34,7 @@
  grpdelay 
  impz 
  zplane 
+ fwhm
 Filter conversion
  ac2poly 
  poly2ac 

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/main/signal/inst/fwhm.m	Sat Jul 11 19:20:27 2009 +0000
@@ -0,0 +1,53 @@
+%% -*- texinfo -*-
+%% @deftypefn {Function File} {} fwhm (@var{f})
+%% @deftypefnx{Function File} {} fwhm (@var{x}, @var{f})
+%% Return the full width at half maximum if a given signal.
+%%
+%% The full width at half maximum is an expression of the extent of a signal,
+%% defined as the difference between the two extremal points of the signal where
+%% it equals half of its maximum value.
+%%
+%% The signal is given by the vector @var{f} with optional @math{x}-values
+%% @var{x}. If the latter is not given, it defaults to the indexes of @var{f}.
+%%
+%% If the full width at half maximum is not defined, the function returns 0.
+%% @seealso{std}
+%% @end deftypefn
+
+%% This program is public domain.
+%% Author: Christophe Cossou
+
+function retval = fwhm (x, f)
+  %% Check input
+  if (nargin == 0)
+    error ('fwhm: not enough input arguments');
+  elseif (nargin == 1)
+    f = x;
+    x = 1:length (f);
+  end
+
+  if (numel (x) != numel (f))
+    error ('fwhm: number of elements does not match');
+  end
+
+  %% Locate maximum
+  fmax = max (f);
+  f_renorm = f - 0.5 * fmax;
+
+  ind = find (f_renorm(1:end-1) .* f_renorm (2:end) <= 0);
+
+  %% If the product is negative, this means that the 'half-maximum' is between
+  %% theses two values
+  if (length (ind) == 2)
+    %% We make a linear regression between the two values to get a more precise
+    %% estimation of the fwhm. 
+    x1 = (0.5 * fmax - f (ind (1) + 1)) * (x (ind (1) + 1) - x (ind (1))) ...
+       / (f (ind (1) + 1) - f (ind (1))) + x (ind (1) + 1);
+    x2 = (0.5 * fmax - f (ind (end) + 1)) * (x (ind (end) + 1) - x (ind (end))) ...
+       / (f (ind (end) + 1) - f (ind (end))) + x (ind (end) + 1);
+    retval = x2 - x1;
+  else
+    % warning ('fwhm: full width at half maximum is not defined. FWHM is set to 0');
+    retval = 0;
+  end
+