Re: FindRoot
- To: mathgroup at smc.vnet.net
- Subject: [mg8822] Re: [mg8793] FindRoot
- From: Allan Hayes <hay at haystack.demon.co.uk>
- Date: Fri, 26 Sep 1997 00:33:45 -0400
- Sender: owner-wri-mathgroup at wolfram.com
Torbjorn Randahl <ekatra at eka.ericsson.se>
[mg8793] FindRoot
writes as below the line *****
Torbjorn:
Changing the input slightly (giving two initial values as suggested
in the message that you got)I get (on a 33 MHz NeXT slab)
FindRoot[yd == 71, {f, 300000,300001}]//Timing
{0.124536 Second,{f->714877.}}
Allan Hayes
hay at haystack.demon.co.uk
http://www.haystack.demon.co.uk/training.html
voice:+44 (0)116 2714198
fax: +44 (0)116 2718642
Leicester, UK
********************************
Hi!
Mma can't find f (the frequency) for a value of yd, my HP48GX find it
within 6 seconds!
yd is the Real part of the root of (r+sl)sc
r changes with f, the same with l. c and d are constants
s is jw (complex)
This is the Mma run:
yd := (20*d*Re[Sqrt[(r + l*s)*s*c]])/Log[10]
s := f*I*2*Pi
r := (((f*2*Pi)^1.198*2.18)/10^9 + 0.276)*1000
l := (587 - (f*92.37)/10^6)/10^6
c = 50/10^9
d=3.5
FindRoot[yd == 71, {f, 300000, 30000, 1.1*10^6}]
FindRoot::"frjc":
"Could not symbolically find the Jacobian of
{-71+0.0170395 Re[<<1>>]}. Try giving two starting
values for each variable."
(I've tried Solve,Nsolve also)
If I then set f to 714880 (from my HP48GX)
f:=714880
yd
71.0002
So if I put in the ansewer Mma gives the right result of yd!
How should I Solve this?
best regards
Tobbe Randahl
Ericsson Components AB
Kista
Sweden
email: ekatra at eka.ericsson.se
--
Torbjorn Randahl