Help writing a simple function

I'm new to functions, and I was wondering how you would write a simple if, then function.

if x<4, then f(x)=-1
if 4<=x<=4 then f(x)=cos(x)
if x>4 then f(x)=1

%when an x is entered, it should give f(x) as the output. %Thank you.

Answer 1

[Azzi Abdelmalek]

Read the documentation, you will find examples if, elseif, else

Answer 2

[David Sanchez]

You should do as Azzi Abdelmalek says, anyway, here is your code:

if x<4
    f = -1;
elseif  x>=4 && x<=4
    f = cos(x);
else
    f = 1;
end

Answer 3

[Andrei Bobrov]

function out = f(x)
    out = sign(x-4);
    out(~out) = cos(4);
end

use

>> out = f([- 3 5 6 4 -2 3 1 4])
out =

    -1.00000   1.00000   1.00000  -0.65364  -1.00000  -1.00000  -1.00000  -0.65364