POLPHASE
* Purpose:
Phase plot of a continuous-time polynomial
* Syntax:
POLPHASE(P)
* Description:
cf. the on-line help
* Example
With the instruction
polphase(1+5*s+10*s^2+10*s^3+5*s^4+s^5)}
we obtain a phase plot intersecting the real and imaginary axes 5
times. Moreover its argument is strictly increasing. Consequently, the
input polynomial is stable.
Now suppose that q=0.5. With the instruction
polphase(1+5*s+10*s^2+10*s^3+0.5*s^4+s^5)}
we obtain a phase plot intersecting the real and imaginary axes 3
times, so the input polynomial is not stable.
* Algorithm:
The phase plot is computed by evaluating the input polynomial at 1000
equidistant points along the imaginary axis. The maximum frequency is
set to twice the maximum modulus of the roots of the even and odd
parts of the input polynomial. To improve readability of the phase
plot, the modulus is scaled at the power 1/d where d is the degree
of the input polynomial.
* Diagnostics:
The macro produces error messages if
. the input polynomial is constant (zero degree)
. the input polynomial is discrete-time
* See also:
ISSTABLE