For these function the eigenvalue may be a complex number with a positive imaginary part.
This does not totally remove the degeneracy since any solution when multiplied by a complex number with magnitude 1 will also satisfy this criterion.
These normalized residues are a priori free complex number s depending on the considered pole of v (respectively b).
Note that becomes a complex number in the case of instabilities.
The constructor (:+) forms a complex number from its real and imaginary rectangular components.
For this we need to think of r as a complex number.
However, the tuple constructor that is used to pack the real and imaginary parts of the complex number forces a lazy context for its arguments.
For every r there exist two real number solutions, or two complex number solutions or mixed solutions.
