Matlab why is logical not of tilde `~` not mentioned docs?

Question

I have seen some code that uses:

index = findstr('something', 'longer string');
if ~isempty(index)
  % do something
end

I looked up the documentation for MatLab symbols here and it doesn't mention anything about using ~ for converting primitive integer values into boolean. i.e. if index is 10 or if it is [] then isempty will return 0 or 1 which will be converted to 1 or 0 with the ~ operator. However this use case isn't mentioned in the docs. Is this a legitimate way of performing negation. Is there another way of achieving this negation?

Is A==0 really better than ~A? might be relevant.

Divakar
– Divakar

2015-10-22 18:22:14 +00:00
Commented Oct 22, 2015 at 18:22 — Divakar
– Divakar, Commented Oct 22, 2015 at 18:22

the_candyman · Accepted Answer · 2015-10-22 18:03:50Z

2

In the workspace, enter

doc not

or

doc ~

You will have an answer from the documentation of Matlab.

answered Oct 22, 2015 at 18:03

the_candyman

1,6734 gold badges24 silver badges38 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Brian Lynch · Accepted Answer · 2015-10-22 18:05:19Z

1

This use case is mentioned in the docs exactly where your link points to (see "Not Equal To" and "Logical NOT" under "Tilde -- ~"). You can also enter help ~ in the MATLAB console and get an explanation about usage.

This is the legitimate way of performing negation of a boolean. You can apply it to 0 and 1 to flip them, but it will also treat any non-zero value as a 1.

Another way to perform negation of x would be x = 1 - x, but that only works if x is boolean. So for the code you posted, you could do this:

index = findstr('something', 'longer string');
if 1 - isempty(index)
  % do something
end

answered Oct 22, 2015 at 18:05

Brian Lynch

5425 silver badges13 bronze badges

3 Comments

Andras Deak -- Слава Україні Over a year ago

Note that you can also convert to boolean with logical(10), so you could use 1-logical(x). But that's basically ~x anyway.

AJP Over a year ago

I think the original question is sound. It's not obvious from "To test for inequality values of elements in arrays a and b for inequality, use a~=b" if the tilde is valid to be used with a primitive integer value and what it would produce. The "Logical not" part of the documentation linked to similar just talks about arrays: "To find those elements of an array that are zero, use: ~a". It would be rash to make an assumptions about the return value from an operator on an integer when the only mentioned is of working with arrays.

Brian Lynch Over a year ago

Certainly, and of course most other languages use ! instead of ~. Hope my answer doesn't come across as suggesting it is a bad question.

Collectives™ on Stack Overflow

Matlab why is logical not of tilde `~` not mentioned docs?

2 Answers 2

Comments

3 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

3 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related