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