MatLab Logical answer always 1

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Matlab_Student
Matlab_Student on 26 Sep 2017
Commented: Jan on 26 Sep 2017
I have 2017b installed on my mac. Below is the confusing part:.....
>> islogical(5<7)
ans =
logical
1
>> islogical(5>7)
ans =
logical
1
  1 Comment
Stephen23
Stephen23 on 26 Sep 2017
Edited: Stephen23 on 26 Sep 2017
The MATLAB documentation for islogical states clearly that " tf = islogical(A) returns true if A is a logical array and false otherwise" (emphasis added). It does not state anywhere on the page that islogical tests what the value of the logical array is.
Lets try it. Both true and false are scalar logical arrays, so we would expect them both to return true if we test if they are logical arrays:
>> islogical(true)
ans = 1
>> islogical(false)
ans = 1
>>
So no surprises there: a logical array is a logical array.

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Accepted Answer

Cedric Wannaz
Cedric Wannaz on 26 Sep 2017
Edited: Cedric Wannaz on 26 Sep 2017
Yes, all these tests (relational operators) return a logical, which is a value that is true (1) or false (0).
But:
>> 5 < 7 % Returns true (symbolized by 1).
ans =
logical
1
>> 5 > 7 % Returns false (symbolized by 0).
ans =
logical
0
  4 Comments
Jan
Jan on 26 Sep 2017
In other words: islogical(x) is equivalent to:
strcmp(class(x), 'logical')
or
isa(x, 'logical')
Remark: isa() is surprisinlgy slow: it needs about 4 times longer than the strcmp method.

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