[Octave-bug-tracker] [bug #29942] concatenating with an empty scalar gives an error

[Jaroslav Hajek]

Follow-up Comment #24, bug #29942 (project octave):

Ugh. That was hard, but this patch brings [] pretty close:
http://hg.savannah.gnu.org/hgweb/octave/rev/53253f796351

octave:1> load t.mat
octave:2> t1{1} = test_cat (@(x,y) [x,y]);
octave:3> t1{2} = test_cat (@(x,y) [x;y]);
octave:4> t1{3} = test_cat (@(x,y) [x;y;x]);
octave:5> t1{4} = test_cat (@(x,y) [x,y,x]);
octave:6> t1{5} = test_cat (@(x,y) horzcat (x, y));
octave:7> t1{6} = test_cat (@(x,y) vertcat (x, y));
octave:8> t1{7} = test_cat (@(x,y) cat (1, x, y));
octave:9> t1{8} = test_cat (@(x,y) cat (2, x, y));
octave:10> t1{9} = test_cat (@(x,y) cat (3, x, y));
octave:11> 
octave:11> t1 = cat (3, t1{:}); 
octave:12> m = cellfun (@isequal, t, t1);
octave:13> squeeze(all(all(m,1),2))
ans =

   1
   1
   0
   0
   0
   0
   1
   1
   1


Regarding the mismatches of 3, 4, they are:

octave:15> [i,j] = find(!m(:,:,3))
i =  3
j =  2
octave:16> [i,j] = find(!m(:,:,4))
i =  2
j =  3

Hmmm. This corresponds to this case:

octave:17> x = zeros(1,0); y = zeros(0,1);
octave:18> [x;y;x]
ans = [](1x0)
octave:19> [[x;y];x]
ans = [](1x0)

can you verify that these two expressions give a different result in Matlab?

This suggests that strictly incremental accumulation of the dimension vector
is not enough to mimick Matlab. Duh.

I hope everyone agrees that these corner cases are anal enough to be beyond
Octave's scope of Matlab compatibility.

The rest two mismatches (5 and 6) correspond to vertcat/horzcat, which now
simply call cat(). I'll address those in a separate changeset.

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