NetNews Usenet Archive 1992 #18/NN_1992_18.iso/spool/comp/sys/hp48/4361

Text File | 1992-08-21 | 2.1 KB | 52 lines

Newsgroups: comp.sys.hp48
Path: sparky!uunet!van-bc!ubc-cs!unixg.ubc.ca!ochealth
From: [e-mail] (ochealth)
Subject: Re: Hp48 and TI85 compared
Message-ID: <[e-mail]>
Sender: [e-mail] (Usenet News Maintenance)
Nntp-Posting-Host: unixg.ubc.ca
Organization: University of British Columbia, Vancouver, B.C., Canada
References: <[e-mail]> <[e-mail]> <[e-mail]>
Date: Sat, 22 Aug 1992 03:49:50 GMT
Lines: 39

In article <[e-mail]> mheiskan@.vipunen.hut.fi writes:
>In article <[e-mail]> [e-mail] (ochealth) writes:
>
>>   Can the TI85 find roots of complex polynomials? Wickes can't, but with a
>>   little trick (any Wayne`s POLY utils) it can.
>


OK, it's pretty simple. Since Bill Wickes' polynomial root finder is so fast,
this trick *crudely* lets it find roots to polynomials with complex coefficients
(instead of just real coefficients).

You need Wayne's or *somebody's* poly utils to make this  easy.

Let Z = [ coefficiients array ], which is a complex vector.
let Z* = conj(Z) (use HP's built in CONJ)

then let Z' = ZZ* ie the original polynomial mulitpled by its conjugate
Z' is gauranteed to have purely real coefficients. So use RE on Z'
and feed that into Wickes' fast root finder. You will get 2*N roots, where
N=degree(Z). N roots will be correct. N roots will be wrong, or repeated roots.
To find the good roots and the bogus ones, go through and evaluate Z(rk) for
k=1 to N.

I'll be the first to admit that this is a kludge, but since Wickes' root
finder is so fast, this technique still finds complex roots faster than
other programs.

>What's the trick? (I don't have Wayne's POLY utils.)
>
>--
>--> [e-mail]

jpm
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