Trouble with FindRoot
- To: mathgroup at smc.vnet.net
- Subject: [mg8787] Trouble with FindRoot
- From: Torbjorn Randahl <ekatra at eka.ericsson.se>
- Date: Thu, 25 Sep 1997 12:26:21 -0400
- Organization: Ericsson Components AB NL/ME
- Sender: owner-wri-mathgroup at wolfram.com
Hi!
Why does this not work on MMA? My HP48GX solves this equation
whitin 6 seconds!
I've tried with Solve and NSolve also...
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}]
Out=
FindRoot::"frjc":
"Could not symbolically find the Jacobian of .
{-71+0.0170395 Re[<<1>>]}
Try giving two starting values for each variable.
r is real changing with f, the same with l
s is jw (complex)
c & d are constants
It looks like the solver beleves that there are several unknown
variables.
if I set f to (from my HP48GX)
In[55]:=
f:=714880
In[56]:=
yd
Out[56]=
71.0002
How should I have Solved this??
Torbjorn Randahl
Ericsson Components AB
Kista
Sweden