csgn — Returns the sign of a vector of real of complex values.
s = csgn(z)
The vector of values on which we want to compute the sign.
If the real part is not equal to zero:
+1 if the real part of an element if positive
-1 if the real part of an element if negative
If the real part is equal to zero:
+1 if the imaginary part of an element if positive
-1 if the imaginary part of an element if negative
if the element is equal to zero, then returns %nan