Purpose
To compute the coefficients of a real polynomial P(x) from its zeros. The coefficients are stored in decreasing order of the powers of x.Specification
SUBROUTINE MC01PY( K, REZ, IMZ, P, DWORK, INFO )
C .. Scalar Arguments ..
INTEGER INFO, K
C .. Array Arguments ..
DOUBLE PRECISION DWORK(*), IMZ(*), P(*), REZ(*)
Arguments
Input/Output Parameters
K (input) INTEGER
The number of zeros (and hence the degree) of P(x).
K >= 0.
REZ (input) DOUBLE PRECISION array, dimension (K)
IMZ (input) DOUBLE PRECISION array, dimension (K)
The real and imaginary parts of the i-th zero of P(x)
must be stored in REZ(i) and IMZ(i), respectively, where
i = 1, 2, ..., K. The zeros may be supplied in any order,
except that complex conjugate zeros must appear
consecutively.
P (output) DOUBLE PRECISION array, dimension (K+1)
This array contains the coefficients of P(x) in decreasing
powers of x.
Workspace
DWORK DOUBLE PRECISION array, dimension (K)
If K = 0, this array is not referenced.
Error Indicator
INFO INTEGER
= 0: successful exit;
< 0: if INFO = -i, the i-th argument had an illegal
value;
> 0: if INFO = i, (REZ(i),IMZ(i)) is a complex zero but
(REZ(i-1),IMZ(i-1)) is not its conjugate.
Method
The routine computes the coefficients of the real K-th degree
polynomial P(x) as
P(x) = (x - r(1)) * (x - r(2)) * ... * (x - r(K))
where r(i) = (REZ(i),IMZ(i)).
Note that REZ(i) = REZ(j) and IMZ(i) = -IMZ(j) if r(i) and r(j)
form a complex conjugate pair (where i <> j), and that IMZ(i) = 0
if r(i) is real.
Numerical Aspects
None.Further Comments
NoneExample
Program Text
NoneProgram Data
NoneProgram Results
None