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