Author 
Comment/Response 
Bill Simpson

01/18/13 2:05pm
In Response To 'Re: Re: Solve equation(s) with a List as Variable'  In[1]:= mag={5*10^9,9*10^9,13*10^9,17*10^9};
w=0.005;
d:=148*10^(9);
mu0:=4*Pi*10^(7);
B:=5/10000;
Map[FindRoot[(w*d*B+mu0*#)/(2*w*B)x*Tanh[d/(2*x)],{x,1*10^8}]&,mag]
From In[5]:= FindRoot::lstol: The line search decreased the step size to within tolerance specified by AccuracyGoal and PrecisionGoal but was unable to find a sufficient decrease in the merit function. You may need more than MachinePrecision digits of working precision to meet these tolerances.
Out[5]= {{x>0.0785054},{x=>0.0321371},{x>0.00850291},{x>0.0148893}}
Without the exact numbers for a particular example I'm sort of left with "I typed some stuff in, some stuff came out, some stuff is wrong, what do I do?"
If I just the FindRoot wrapped around the Map, replace the 0.005 with 5/1000 and simplify then I get expressions like
200000*(37/100000000000000 + Pi/500000000000000)  x*Tanh[37/(500000000*x)]
It isn't clear to me if there are zeros of that.
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