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

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Author Comment/Response
Bill Simpson
01/18/13 2:05pm

In Response To 'Re: Re: Solve equation(s) with a List as Variable'
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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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Subject (listing for 'Solve equation(s) with a List as Variable')
Author Date Posted
Solve equation(s) with a List as Variable Markus 01/17/13 12:15pm
Re: Solve equation(s) with a List as Variable Bill Simpson 01/17/13 10:19pm
Re: Re: Solve equation(s) with a List as Variable Markus 01/18/13 09:22am
Re: Re: Re: Solve equation(s) with a List as Va... Bill Simpson 01/18/13 2:05pm
Re: Re: Re: Re: Solve equation(s) with a List a... Markus 01/19/13 06:08am
Re: Re: Re: Re: Re: Solve equation(s) with a Li... Bill Simpson 01/20/13 9:02pm
Re: Re: Re: Re: Re: Solve equation(s) with a Li... Bill Simpson 01/20/13 9:30pm
Re: Re: Re: Re: Re: Re: Solve equation(s) with ... Markus 01/21/13 12:25pm
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