NOT logical operators???

Pls help I dont understand the last line when i typed it in matlab

when A = [ 1 2 3 ]

A>2 is 0 0 1

but ~A is 0 0 0

I don't get the last part. shouldn't it be 1 1 0??? and if i put ~~ it is still 0 0 0.

what does this mean??

Thanks

Answer 1

[Walter Roberson]

It means you tested two different things. In the first one you tested (A>2) . In the second one you tested ~A, which is the same thing as ~(A~=0) which is the same thing as (A==0)

If you wanted the negation of (A>2) then you would use ~(A>2)

[Natalia Wong]

i meant ~(A>2) why is the answer 0 0 0 . I dont' get it thanks

[Walter Roberson]

I would suggest to you that what you typed in was

~A>2

The ~ operator has higher priority than the > operator, so that would be evaluated as

(~A)>2

and ~A is the same as (A~=0)

so ~A>2 is the same as (A~=0)>2

The result of (A~=0) is always 0 (false) or 1 (true), and neither 0 nor 1 are >2, so no matter what the input is, ~A>2 is always going to be false (or an error for other reasons.)

You need ~(A>2)

[Stephen23]

And the reason why this is so is explained here:

http://www.mathworks.com/help/matlab/matlab_prog/operator-precedence.html

which clearly shows that logical negation has a higher precedence than the relational operators. This is why Walter Roberson's answer is correct.