Syntax bug R2011a: x ==y

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Daniel Shub
Daniel Shub il 20 Set 2012
In coming up with an answer to another question I was playing around and think I found a bug in R2011a in Linux. Can anyone explain
>> x = randi(2, 10, 1)-1; % Dummy data
>> x == 0;
>> x ==0;
??? Error: "x" was previously used as a variable,
conflicting with its use here as the name of a function or command.
See MATLAB Programming, "How MATLAB Recognizes Function Calls That Use
Command Syntax" for details.
The 2nd and 3rd line differ in the presence (works) and absence (errors) of a space after ==. I cannot think of why the space matters. The error message also doesn't make sense to me. Is this reproducible? Is it a bug?
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Javier
Javier il 20 Set 2012
Modificato: Javier il 20 Set 2012
Hello Tom
You have to give an additional space in the second x definition. No error in Matlab R2012a for Mac
>> x = randi(2, 10, 1)-1; % Dummy data
>> x == 0;
>> x == 0; %differs from x ==0; or
>> x=randi(2, 10, 1)-1; % Dummy data
>> x==0;
>> x==0;
Daniel Shub
Daniel Shub il 20 Set 2012
@Javier, but I am specifically asking about the odd case of x ==0 (with a space before, but not after, ==). I think of MATLAB as being generous about the usage of white space. This is a case where you need to follow a few rules.

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Sean de Wolski
Sean de Wolski il 20 Set 2012
Modificato: Sean de Wolski il 20 Set 2012
It is seeing ==0 as a string and x as a function. I.e. equivalent to:
x '==0';
This is not a bug. From the doc:
Space after an identifier, but not after a potential operator, implies a function call using command syntax. For example:
ls ./d
Reference
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Sean de Wolski
Sean de Wolski il 20 Set 2012
Modificato: Sean de Wolski il 20 Set 2012
Hence it throws the error for the conflict (it wants to call x as a function but can't because it's a variable)
Also:
x('==0') is equivalent to >>x '==0' and apparently >>x ==0
Jan
Jan il 5 Mar 2013
The different behavior between "x == 0" and "x ==0" might be a documented bug. The smartness of Matlab intelligent auto-parsing of the non-functional form exceeds the intuition of programmers. Now I'm unsure avour "x>0" and "x >=0" also.
The number of forum users struggeling with save(FileName) compared to save FileName decreases. I assume the newer documentation is better.

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