FindRoot
- To: mathgroup at smc.vnet.net
- Subject: [mg8793] FindRoot
- From: Torbjorn Randahl <ekatra at eka.ericsson.se>
- Date: Thu, 25 Sep 1997 12:26:28 -0400
- Organization: Ericsson Components AB NL/ME
- Sender: owner-wri-mathgroup at wolfram.com
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