[Octave-bug-tracker] [bug #49759] Inconsistent concatenation with cat, horzcat, vertcat, and []

[Amro]

URL:
  <http://savannah.gnu.org/bugs/?49759>

                 Summary: Inconsistent concatenation with cat, horzcat,
vertcat, and []
                 Project: GNU Octave
            Submitted by: amro_octave
            Submitted on: Sat 03 Dec 2016 02:53:35 PM EET
                Category: Octave Function
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Incorrect Result
                  Status: None
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 4.2.0
        Operating System: Any

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Details:

Concatenating an empty matrix 0x0 with a cell array produce the wrong result,
and is inconsistent depending on how we do it.

For example, in Octave 4.2.0 I get this:


>> A = [];
>> B = {1; 2};
>> C = [A; B]
C = 
{
  [1,1] =  1
  [2,1] =  2
}
>> C = cat(1, A, B)
C = 
{
  [1,1] = [](0x0)
  [2,1] =  1
  [3,1] =  2
}
>> C = vertcat(A, B)
C = 
{
  [1,1] = [](0x0)
  [2,1] =  1
  [3,1] =  2
}
>> C = [A B]
C = 
{
  [1,1] =  1
  [2,1] =  2
}
>> C = cat(2, A, B)
error: cat: dimension mismatch
>> C = horzcat(A, B)
error: horzcat: cat: dimension mismatch


On the other hand, in MATLAB R2016b I get this:


>> A = [];
>> B = {1; 2};
>> C = [A; B]
C =
  2x1 cell array
    [1]
    [2]
>> C = cat(1, A ,B)
C =
  2x1 cell array
    [1]
    [2]
>> C = vertcat(A, B)
C =
  2x1 cell array
    [1]
    [2]
>> C = [A B]
C =
  2x1 cell array
    [1]
    [2]
>> C = cat(2, A, B)
C =
  2x1 cell array
    [1]
    [2]
>> C = horzcat(A, B)
C =
  2x1 cell array
    [1]
    [2]


So it seems that in Octave using square-brackets to concatenate gives
different results than using the equivalent cat/horzcat/vertcat.

Note that if you replace the empty array with an empty cell array (i.e A={}
instead of A=[]) then Octave behaves correctly and give the same results as
MATLAB in all cases.





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