Purpose
To compute the coefficients of a complex polynomial P(x) from its zeros.Specification
SUBROUTINE MC01OD( K, REZ, IMZ, REP, IMP, DWORK, INFO )
C .. Scalar Arguments ..
INTEGER INFO, K
C .. Array Arguments ..
DOUBLE PRECISION DWORK(*), IMP(*), IMZ(*), REP(*), 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.
REP (output) DOUBLE PRECISION array, dimension (K+1)
IMP (output) DOUBLE PRECISION array, dimension (K+1)
These arrays contain the real and imaginary parts,
respectively, of the coefficients of P(x) in increasing
powers of x. If K = 0, then REP(1) is set to one and
IMP(1) is set to zero.
Workspace
DWORK DOUBLE PRECISION array, dimension (2*K+2)
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.
Method
The routine computes the coefficients of the complex 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)), using real arithmetic.
Numerical Aspects
None.Further Comments
NoneExample
Program Text
* MC01OD EXAMPLE PROGRAM TEXT
* Copyright (c) 2002-2010 NICONET e.V.
*
* .. Parameters ..
INTEGER NIN, NOUT
PARAMETER ( NIN = 5, NOUT = 6 )
INTEGER KMAX
PARAMETER ( KMAX = 10 )
* .. Local Scalars ..
INTEGER I, INFO, K
* .. Local Arrays ..
DOUBLE PRECISION DWORK(2*KMAX+2), IMP(KMAX+1), IMZ(KMAX),
$ REP(KMAX+1), REZ(KMAX)
* .. External Subroutines ..
EXTERNAL MC01OD
* .. Executable Statements ..
*
WRITE ( NOUT, FMT = 99999 )
* Skip the heading in the data file and read the data.
READ ( NIN, FMT = '()' )
READ ( NIN, FMT = * ) K
IF ( K.LT.0 .OR. K.GT.KMAX ) THEN
WRITE ( NOUT, FMT = 99995 ) K
ELSE
READ ( NIN, FMT = * ) ( REZ(I), IMZ(I), I = 1,K )
* Compute the coefficients of P(x) from the given zeros.
CALL MC01OD( K, REZ, IMZ, REP, IMP, DWORK, INFO )
*
IF ( INFO.NE.0 ) THEN
WRITE ( NOUT, FMT = 99998 ) INFO
ELSE
WRITE ( NOUT, FMT = 99997 )
WRITE ( NOUT, FMT = 99996 )
$ ( I, REP(I+1), IMP(I+1), I = 0,K )
END IF
END IF
STOP
*
99999 FORMAT (' MC01OD EXAMPLE PROGRAM RESULTS',/1X)
99998 FORMAT (' INFO on exit from MC01OD = ',I2)
99997 FORMAT (' The coefficients of the polynomial P(x) are ',//' powe',
$ 'r of x real part imag part ')
99996 FORMAT (2X,I5,8X,F9.4,5X,F9.4)
99995 FORMAT (/' K is out of range.',/' K = ',I5)
END
Program Data
MC01OD EXAMPLE PROGRAM DATA 5 1.1 0.9 0.6 -0.7 -2.0 0.3 -0.8 2.5 -0.3 -0.4Program Results
MC01OD EXAMPLE PROGRAM RESULTS
The coefficients of the polynomial P(x) are
power of x real part imag part
0 2.7494 -2.1300
1 -1.7590 -5.4205
2 0.0290 2.8290
3 -1.6500 -1.7300
4 1.4000 -2.6000
5 1.0000 0.0000
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