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Re: Evaluating 'or' statements: bug or feature?
From: |
David Bateman |
Subject: |
Re: Evaluating 'or' statements: bug or feature? |
Date: |
Wed, 09 Jul 2008 11:15:20 +0200 |
User-agent: |
Thunderbird 2.0.0.12 (X11/20080306) |
Bill Denney wrote:
> Andy Sinton wrote:
>
>> I've encountered this issue twice when running .m files in Octave
>> (3.01, windows).
>> With an 'or' statement such as
>>
>> if u > v | someFunction(b)
>>
>> chokes if there is no variable 'b', even though it is true that u > v.
>> I guess Matlab stops evaluating 'or' statements when it hits the
>> first true statement and Octave keeps going?
>> Is there a reason for this bug/feature?
>> Thanks!
>>
>
> Hi Andy,
>
> This is a topic that comes up relatively often. The short answer is
> that if you want a shortcutting or, you need to use the double pipe
> (||). The single pipe is an element-wise or while double is a boolean
> or. Assuming that u, v, and the output of someFunction(b) are all
> scalars, you are probably wanting
>
> u > v || someFunction(b)
>
> Have a good day,
>
>
Also read
http://www.gnu.org/software/octave/FAQ.html#MATLAB-compatibility
and in particular the section on short-circuit operators, for the
explanation why matlab's behavior in this case is a really bad idea, and
why they finally changed their might and also accepted "||" as the
short-circuit operator.
D.
--
David Bateman address@hidden
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