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Student Support Forum > General > > "Solve equation(s) with a List as Variable"

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Original Message (ID '258014') By Bill Simpson:
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.