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[Octave-bug-tracker] [bug #53897] poly of conjugate complex pairs should
From: |
Rik |
Subject: |
[Octave-bug-tracker] [bug #53897] poly of conjugate complex pairs should return a real polynomial |
Date: |
Sat, 13 Oct 2018 12:37:01 -0400 (EDT) |
User-agent: |
Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:62.0) Gecko/20100101 Firefox/62.0 |
Update of bug #53897 (project octave):
Status: None => Need Info
_______________________________________________________
Follow-up Comment #1:
The algorithm in poly.m uses a for loop and repeated multiplications. It
could be something as simple as, with the inversion of matrices, using
balance() to put the largest factors first, etc.
In this example, if I use sort on the input x then the conjugates are paired
and the result of poly is entirely real without spurious imaginary terms.
See the session below
octave:25> n = 3;
octave:26> fr = 436;
octave:27> x = 1i * 2 * pi * fr * [-n:-1 1:n]
x =
-0.0 - 8218.4i -0.0 - 5478.9i -0.0 - 2739.5i 0.0 + 2739.5i
0.0 + 5478.9i 0.0 + 8218.4i
octave:28> N = poly (x)
N =
Columns 1 through 6:
1.0000e+00 + 0.0000e+00i 0.0000e+00 - 1.8190e-12i 1.0507e+08 +
0.0000e+00i 0.0000e+00 + 1.8311e-04i 2.7597e+15 + 0.0000e+00i 0.0000e+00
+ 2.5600e+02i
Column 7:
1.5216e+22 + 0.0000e+00i
octave:29> x2 = sort (x)
x2 =
-0.0 - 2739.5i 0.0 + 2739.5i -0.0 - 5478.9i 0.0 + 5478.9i
-0.0 - 8218.4i 0.0 + 8218.4i
octave:30> N2 = poly (x2)
N2 =
1.0000e+00 0.0000e+00 1.0507e+08 0.0000e+00 2.7597e+15 0.0000e+00
1.5216e+22
octave:31> roots (N2)
ans =
-0.0 + 8218.4i
-0.0 - 8218.4i
-0.0 + 5478.9i
-0.0 - 5478.9i
-0.0 + 2739.5i
-0.0 - 2739.5i
Should we just sort the input vector 'v' after the input validation in
poly.m?
_______________________________________________________
Reply to this item at:
<https://savannah.gnu.org/bugs/?53897>
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- [Octave-bug-tracker] [bug #53897] poly of conjugate complex pairs should return a real polynomial,
Rik <=
- [Octave-bug-tracker] [bug #53897] poly of conjugate complex pairs should return a real polynomial, Marco Caliari, 2018/10/15
- [Octave-bug-tracker] [bug #53897] poly of conjugate complex pairs should return a real polynomial, Rik, 2018/10/15
- [Octave-bug-tracker] [bug #53897] poly of conjugate complex pairs should return a real polynomial, Marco Caliari, 2018/10/16
- [Octave-bug-tracker] [bug #53897] poly of conjugate complex pairs should return a real polynomial, Rik, 2018/10/17
- [Octave-bug-tracker] [bug #53897] poly of conjugate complex pairs should return a real polynomial, Marco Caliari, 2018/10/17
- [Octave-bug-tracker] [bug #53897] poly of conjugate complex pairs should return a real polynomial, Rik, 2018/10/17
- [Octave-bug-tracker] [bug #53897] poly of conjugate complex pairs should return a real polynomial, Marco Caliari, 2018/10/18
- [Octave-bug-tracker] [bug #53897] poly of conjugate complex pairs should return a real polynomial, Marco Caliari, 2018/10/19
- [Octave-bug-tracker] [bug #53897] poly of conjugate complex pairs should return a real polynomial, Markus Mützel, 2018/10/19
- [Octave-bug-tracker] [bug #53897] poly of conjugate complex pairs should return a real polynomial, Marco Caliari, 2018/10/19