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Re: FindRoot vs Solve

  • To: mathgroup at smc.vnet.net
  • Subject: [mg22507] Re: FindRoot vs Solve
  • From: "Bill Bertram" <wkb at ansto.gov.au>
  • Date: Sun, 5 Mar 2000 00:24:46 -0500 (EST)
  • Organization: Australian Nuclear Science and Technology Organisation
  • References: <89ichk$n45@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

F. Mittermayr wrote in message <89ichk$n45 at smc.vnet.net>...
>Why is FindRoot not able to solve an equation using "Degree"? Solve can do
>it.
>
>In[]=
>
>Solve[28. Cos[phi Degree] - 20. == 0, phi]
>FindRoot[28. Cos[phi1 Degree] - 20. == 0, {phi1, 0.1, 0.1, 90.}]
>
>Out[]=
>
>{{phi->-44.4153},{phi->44.4153}}
>{phi1->96.7112}


Dear F.

FindRoot does work provided you give an appropriate initial guess for phi1.
Try for example

              FindRoot[28. Cos[phi1 Degree] - 20. == 0, {phi1, 20, 0.1,
90.}]

and you'll find it gives the correct solution.

Cheers,

 Bill





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