[Octave-bug-tracker] [bug #43098] "if (array)" inconsistent with matlab (which is inconsistent with itself)

[Colin Macdonald]

URL:
  <http://savannah.gnu.org/bugs/?43098>

                 Summary: "if (array)" inconsistent with matlab (which is
inconsistent with itself)
                 Project: GNU Octave
            Submitted by: cbm
            Submitted on: Thu 28 Aug 2014 09:32:19 AM GMT
                Category: Libraries
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Matlab Compatibility
                  Status: None
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: dev
        Operating System: GNU/Linux

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Details:

Personally, I think this should raise a warning, telling people we are
defaulting "if (all(array))".  IMHO, "if (array)" is almost certainly a bug in
the user's code (she expected a scalar).

Nonetheless that is not what Matlab does.  What they do is contradictory to
their docs.  What their docs say is weird.


%% two easy cases

a = [1 1 1];
if (a), disp('got it right'); end
if (a), assert(true); else, assert(false); end

a = [1 0 1];
if (a), disp('got it wrong'); else, disp('got it right'); end
if (a), assert(false); else, assert(true); end

%% now the harder ones

a = [1 0+1i 1];
all(a)
if (a), disp('true??'); else, disp('false??'); end

a = [1 1+1i 1];
all(a)
if (a), disp('true, good'); else, disp('false, bad'); end

a = [1i 2i];
all(a)
if (a), disp('true??'); else, disp('false??'); end

%% Matlab:
% all of these give:
% error <Complex values cannot be converted to logicals>
% This contradicts their documentation as "help if" says:
%   > The statements are executed if the real part of the
%   > expression has all non-zero elements.
% (tested on 2008a and 2014a)

%% Octave:
% evaluates to true.  Is this documented?


Please don't change it to Matlab's documented behaviour :)




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