In circuit and control theory, the rational strictly positive real functions (SPR functions) are of high interest. Their standard form is \(H(s)= p(s)/q(s)\), where \(s\) stands for the complex variable. The paper provides two important answers to the theory of SPR functions: a) how to find (algorithmically) \(p(s)\) for a given \(q(s)\) which is strictly Hurwitz polynomial; b) the answer a) when \(q(s)\) is not a fixed polynomial as in a) but it is subjected to some parameter uncertainties. The derivation of the aforementioned answers makes use of some interlacing properties of zeros of the even and of the odd parts of the two polynomials. We think the paper is a good contribution in the area of control and circuit theory.