what will be displayd and why?

-------------------------------------

if (x)
    disp('true');
else
    disp('false');
end;
if (~x)
    disp('true');
else
    disp('false');
end;

----------------------------------------

For the case x=[0 0 0 0]

and for the case x=[0 1 0 1]

[Adam]

Can't you just run the code to find out what is displayed?

You should generally use either 'all' or 'any' around a vector of logicals in an if statement though to avoid unexpected behaviour.

Answer 1

[Stephen23]

This is explained quite clearly in the if documentation: "An expression is true when its result is nonempty and contains only nonzero elements (logical or real numeric). Otherwise, the expression is false."

Which means:

• [0,0,0,0] is false: all values are zero
• [0,1,0,1] is false: some values are zero
• ~[0,0,0,0]=[1,1,1,1] is true: contains only nonzero elements
• ~[0,1,0,1]=[1,0,1,0] is false: some values are zero

Note that the definition defines a true expression as "contains only nonzero elements" but does not give an upper-limit to the number of nonzero elements.

Answer 2

[David Shapiro]

i did it but i did not understand why i got what i got. its a question from a quiz i had.

Answer 3

[Image Analyst]

The all zero case is obvious. x=[0 0 0 0] is false no matter how you look at it - no way it can be true.

But if you have a case like [1 2 0 1] or [0 1 0 1] or [1,2,3,4], it will be true only if ALL of the elements are non-zero.

[David Shapiro]

but what is the condition " if x" means?

[Adam]

In this case (a vector) it seems to be shorthand for

if ( all(x) )

though I never tend to use that shorthand myself as I prefer the explicit use of all or any when using logicals for an if statement.