Re: FindRoot
- To: mathgroup at smc.vnet.net
- Subject: [mg8812] Re: [mg8793] FindRoot
- From: David Withoff <withoff>
- Date: Fri, 26 Sep 1997 00:33:37 -0400
- 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!
This is because you asked your calculator to do a different calculation
than you asked Mathematica to do. The warning message in the following
calculation reflects the fact that the input is not a differentiable
function.
In[1]:= yd := (20*d*Re[Sqrt[(r + l*s)*s*c]])/Log[10]
In[2]:= s := f*I*2*Pi
In[3]:= r := (((f*2*Pi)^1.198*2.18)/10^9 + 0.276)*1000
In[4]:= l := (587 - (f*92.37)/10^6)/10^6
In[5]:= c = 50/10^9;
In[6]:= d=3.5;
In[7]:= FindRoot[yd == 71, {f, 300000, 30000, 1.1*10^6}]
FindRoot::frjc:
Could not symbolically find the Jacobian of
{-71 + 0.0170395 Re[Sqrt[I <<2>>]]}. Try giving two starting values for
each variable.
6
Out[7]= FindRoot[yd == 71, {f, 300000, 30000, 1.1 10 }]
> How should I Solve this?
Try giving two starting values for the variable, as suggested
in the warning message.
In[8]:= FindRoot[yd == 71, {f, 30000, 1.1*10^6}]
Out[8]= {f -> 714877.}
This calculation finishes in a lot less than 6 seconds.
Dave Withoff
Wolfram Research