polystab - Stabilize polynomial
Syntax
b = polystab(a)
Description
polystab stabilizes a polynomial with respect
to the unit circle;
it reflects roots with magnitudes greater than 1 inside the unit circle.
b = polystab(a) returns
a row vector b containing the stabilized polynomial,
where a is a vector of polynomial coefficients,
normally in the z-domain.
Examples
polystab can convert a linear-phase filter
into a minimum-phase
filter with the same magnitude response:
h = fir1(25,0.4);
hmin = polystab(h) * norm(h)/norm(polystab(h));
Algorithm
polystab finds the roots of the polynomial
and maps those roots found outside the unit circle to the inside of
the unit circle:
v = roots(a);
vs = 0.5*(sign(abs(v)-1)+1);
v = (1-vs).*v + vs./conj(v);
b = a(1)*poly(v);
See Also
roots
 | polyscale | | pow2db |  |
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