When I run this function it gives me the following error:

function [S]=Signfunction(f,a,b)
v=a:0.5:b;
n=length(v);
S=zeros(1,n);
for i=1:n
   if f(i)<0
       S(1,i)=-1;
   else
       S(1,i)=1;
   end
end

Signfunction((v.^2)+(2.*v)-9,2,4)
Undefined function or variable 'v'.

Answer 1

[Star Strider]

You have not defined ‘v’ in your script before you called your ‘Signfunction’ function.

Answer 2

[Steven Lord]

In context, you want to evaluate the function ((v.^2)+(2.*v)-9 inside the SignFunction function. To do that, define it as an anonymous function. See the first block of code that defines the anonymous function stored in the variable sqr for an example.

If this is for a homework assignment you could check your results against the sign function included with MATLAB, though it returns 0 where the input vector is 0 instead of returning 1 as your function does.