Error in function at if-elseif

I've got the error Output argument "val" (and maybe others) not assigned during call to "yt". yt(x) funtion:

function [val] = yt(x)
if ((-9<=x) & (x<-3)) | ((3<=x) & (x<=9))
    val = sin(5*x);
elseif (-3<=x) & (x<3)
    val = cos(x) - cos(3) - sin(15);
end

and i call the function using the following

   x = -9:9;
  val = yt(x)

I've got no output from this.

[per isakson]

• Read the documentation on if-else-end
• See Debug a MATLAB Program
• It's good practice to have an else-clause

Answer 1

[Ahmet Cecen]

x is a vector at this point so your comparisons are not resolving to a single true false. I am guessing this is what you meant to do:

 x = -9:9;
 val = yt(x)

 function [val] = yt(x)
    for i = 1:length(x)
        if ((-9<=x(i)) && (x(i)<-3)) || ((3<=x(i)) && (x(i)<=9))
            val(i) = sin(5*x(i));
        elseif (-3<=x(i)) && (x(i)<3)
            val(i) = cos(x(i)) - cos(3) - sin(15);
        end
    end
 end

There are better ways to do this of course, but this is probably the easiest to relate.

[Raul Vaida]

Thank you very much, it worked perfectly this way!