--- a/main/mechanics/inst/private/ind2sub_tril.m	Thu Oct 20 11:15:27 2011 +0000
+++ b/main/mechanics/inst/private/ind2sub_tril.m	Thu Oct 20 12:53:24 2011 +0000
@@ -1,4 +1,4 @@
-%% Copyright (c) 2010 Juan Pablo Carbajal <carbajal@ifi.uzh.ch>
+%% Copyright (c) 2011 Juan Pablo Carbajal <carbajal@ifi.uzh.ch>
 %% 
 %%    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
@@ -15,13 +15,45 @@
 
 %% -*- texinfo -*-
 %% @deftypefn {Function File} {[ @var{r}, @var{c} ] = } ind2sub_tril (@var{N}, @var{idx})
-%% Not documented
+%% Convert a linear index to subscripts of a trinagular matrix.
+%%
+%% An example of trinagular matrix linearly indexed follows
+%%
+%% @example
+%%          N = 4;
+%%          A = -repmat (1:N,N,1);
+%%          A += repmat (diagind, N,1) - A.';
+%%          A = tril(A)
+%%          => A =
+%%              1    0    0    0
+%%              2    5    0    0
+%%              3    6    8    0
+%%              4    7    9   10
+%% @end example
+%%
+%% The following example shows how to convert the linear index `6' in
+%% the 4-by-4 matrix of the example into a subscript.
+%%
+%% @example
+%%          [r, c] = ind2sub_tril (4, 6)
+%%          => r =  2
+%%            c =  3
+%% @end example
+%%
+%% when @var{idx} is a row or column matrix of linear indeces then @var{r} and
+%% @var{c} have the same shape as @var{idx}.
 %%
 %% @seealse{vech, ind2sub, sub2ind_tril}
 %% @end deftypefn
 
 function [r c] = ind2sub_tril(N,idx)
 
+  %% Horrible lengthly check
+  if nargin < 2 ||( !isnumeric (N) && all(size(N)==1) )|| ...
+    !( ismatrix (idx) && any (size (idx)==1) ) 
+    print_usage;
+  endif
+  
   endofrow = 0.5*(1:N) .* (2*N:-1:N + 1);
   c = lookup(endofrow, idx-1)+1;
 
@@ -35,8 +67,14 @@
 
 %!test
 %! A = -repmat (1:N,N,1);
-%! A += A.' + repmat (diagind, N,1));
+%! A += repmat (diagind, N,1) - A.';
+%! A = tril(A);
 %! [r c] = ind2sub_tril (rows(A),1:10);
 %! A_shouldbe = accumarray([r; c]',1:10);
-%! assert (A,A_shouldbe)
+%! assert (A_shouldbe, A)
 
+%!error ind2sub_tril([1 2 3],[4 5 6]); % size is not a scalar
+%!error ind2sub_tril(4,eye(2)); % idx is not a row or column matrix
+%!error ind2sub_tril(4,{1, 2}); % idx is not a row or column matrix
+%!error ind2sub_tril([1 2 3]); % not enough arguments
+

--- a/main/mechanics/inst/private/sub2ind_tril.m	Thu Oct 20 11:15:27 2011 +0000
+++ b/main/mechanics/inst/private/sub2ind_tril.m	Thu Oct 20 12:53:24 2011 +0000
@@ -1,4 +1,4 @@
-%% Copyright (c) 2010 Juan Pablo Carbajal <carbajal@ifi.uzh.ch>
+%% Copyright (c) 2011 Juan Pablo Carbajal <carbajal@ifi.uzh.ch>
 %% 
 %%    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
@@ -15,13 +15,46 @@
 
 %% -*- texinfo -*-
 %% @deftypefn {Function File} {ind = } sub2ind_tril (@var{N}, @var{r}, @var{c})
-%% Not documented
+%% Convert subscripts to a linear index of a trinagular matrix.
+%%
+%% An example of trinagular matrix linearly indexed follows.
 %%
-%% @seealse{vech, sub2ind}
+%% @example
+%%          N = 4;
+%%          A = -repmat (1:N,N,1);
+%%          A += repmat (diagind, N,1) - A.';
+%%          A = tril(A)
+%%          => A =
+%%              1    0    0    0
+%%              2    5    0    0
+%%              3    6    8    0
+%%              4    7    9   10
+%% @end example
+%%
+%% The following example shows how to convert the two-dimensional
+%% index `(3,2)' of the 4-by-4 matrix in the example to a linear index.
+%%
+%% @example
+%%          linear_index = sub2ind_tril (4, 3, 2)
+%%          => linear_index = 6
+%% @end example
+%%
+%% When @var{r} and @var{c} are row or column matrices of subindeces of the same
+%% size then @var{ind} have the same shape as any of them.
+%%
+%% @seealse{vech, sub2ind, ind2sub_tril}
 %% @end deftypefn
 
 function ind = sub2ind_tril(N,r,c)
 
+  %% Horrible lengthly check
+  if nargin < 3 ||( !isnumeric (N) && all(size(N)==1) )|| ...
+    !( ismatrix (r) && any (size (r)==1) ) || ...
+    !( ismatrix (c) && any (size (c)==1) ) || ...
+    any(size(r) != size(c))
+    print_usage;
+  endif
+  
   R = zeros(size(r));
   C = zeros(size(c));
   
@@ -49,3 +82,11 @@
 %! [r c] = ind2sub_tril (N, 1:N*(N+1)/2);
 %! assert (sub2ind_tril (N,r',c'), vech (A)) % Full matrix
 
+%!error sub2ind_tril([1 2 3], [4 5 6], [1 2 3]); % size is not a scalar
+%!error sub2ind_tril(4, eye(2), [1 2]); % r is not a row or column matrix
+%!error sub2ind_tril(4, [1 2], eye(2)); % c is not a row or column matrix
+%!error sub2ind_tril(4, [1 2], [1 2 3]); % c,r not the same size
+%!error sub2ind_tril(4, [1 2 3 ], 1); % c,r not the same size
+%!error sub2ind_tril(4,{1, 2}, {1, 2}); % idx is not a row or column matrix
+%!error sub2ind_tril([1 2 3]); % not enough arguments
+%!error sub2ind_tril(3,[1 2 3]); % not enough arguments