Using AND Operator in “if” statements
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Andrew
on 10 May 2011
Edited: MathWorks Support Team
about 8 hours ago
Hi, When I type the following code: if size([1 2 3])==size([4 5 6]) & size([4 5 6])==size([7 8 9]) 'yes' else 'no' end MATLAB Code Analyzer issues this warning message: "When both arguments are numeric scalars, consider replacing & with && for performance." So, I use && instead of &: if size([1 2 3])==size([4 5 6]) && size([4 5 6])==size([7 8 9]) 'yes' else 'no' end But when I run the updated script, MATLAB displays an error message in the Command Window: ??? Operands to the || and && operators must be convertible to logical scalar values. What can I do to fix this? Thanks in advance. Andrew DeYoung Carnegie Mellon University
7 Comments
Matt Tearle
on 11 May 2011
You're right about IF and vectors, but the Code Analyzer doesn't necessarily know which variables are vectors and which aren't. The & operator is one instance where it can give a message without having to determine that. The str2num vs str2double message is another example. It's vaguely annoying to get a warning, but the Analyzer's just hedging its bets.
[BTW, I'm just passing on the "official" answer here. I was about to submit a request saying, basically, exactly what you've said. But I found an existing discussion, and I've paraphrased the end decision. I'm sure there's more to it than I can skim and pass along.]
Jenny
on 2 Aug 2016
Matt, I still use my notes from your class, and thanks for the help in this question. I needed to get this right.
Accepted Answer
Andrew Newell
about 7 hours ago
Edited: MathWorks Support Team
9 minutes ago
The problem is that size returns a vector: size([1 2 3]) ans = 1 3 Instead, use |numel|: if numel([1 2 3])==numel([4 5 6]) && numel([4 5 6])==numel([7 8 9]) disp('yes') else disp('no') end Or you could use |all(size([1 2 3])==size([4 5 6])| etc. I have also put in the |disp| commands to take care of the other warnings.
More Answers (1)
Sean de Wolski
on 10 May 2011
As an addendum to Andrew's thorough and good solution, you can check the sizes directly:
if(isequal(size([1 2 3]),size([4 5 6])))
disp('yes')
else
disp('no')
end
This will fail if the sizes are not the same but the number of elements (numel) is:
if(isequal(size([1 2 3]),size([4; 5; 6])))
disp('yes')
else
disp('no')
end
3 Comments
Matt Tearle
on 10 May 2011
Another benefit to isequal is that it won't throw an error message in situations where == will (it will just return false). For example
if size(rand(2))==size(rand(3,2,2))
disp('yes')
else
disp('no')
end
will fail because size will return a 3-element vector for a 3-D array. However
if isequal(size(rand(2)),size(rand(3,2,2)))
disp('yes')
else
disp('no')
end
works fine.
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