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## Copyright (C) 2006 Muthiah Annamalai <muthiah.annamalai@uta.edu>
##
## 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 2 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{dist},@var{L}] = {} editdistance(@var{string1},@var{string2},@var{weights})
## computes the Levenshtein edit distance between the two strings.
## @var{string1} and @var{string2}. This operation is symmetrical.
## The optional argument @var{weights} specifies weights for the
## deletion, matched, and insertion operations; by default it is set to
## +1, 0, +1 respectively, so that a least editdistance means a
## closer match between the two strings. This function implements
## the Levenshtein edit distance as presented in Wikipedia article,
## accessed Nov 2006. Also the levenshtein edit distance of a string
## with an empty string is defined to be its length.
##
## The default return value is @var{dist} the edit distance, and
## the other return value @var{L} is the distance matrix.
##
## @example
## @group
## editdistance('marry','marie')
## ##returns value +2 for the distance.
## @end group
## @end example
##
## @end deftypefn
##
function [dist,L]=editdistance(str1,str2,weights)
if(nargin < 2 || (nargin == 3 && length(weights) < 3) )
print_usage();
end
L1=length(str1)+1;
L2=length(str2)+1;
L=zeros(L1,L2);
if(nargin < 3)
g=+1;%insertion
m=+0;%match
d=+1;%deletion
else
g=weights(1);
m=weights(2);
d=weights(3);
end
L(:,1)=[0:L1-1]'*g;
L(1,:)=[0:L2-1]*g;
m4=0;
for idx=2:L1;
for idy=2:L2
if(str1(idx-1)==str2(idy-1))
score=m;
else
score=d;
end
m1=L(idx-1,idy-1) + score;
m2=L(idx-1,idy) + g;
m3=L(idx,idy-1) + g;
L(idx,idy)=min(m1,min(m2,m3));
end
end
dist=L(L1,L2);
return
end
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