Services & Resources / Wolfram Forums / MathGroup Archive
-----

MathGroup Archive 2012

[Date Index] [Thread Index] [Author Index]

Search the Archive

Re: Complex and Solve

  • To: mathgroup at smc.vnet.net
  • Subject: [mg125143] Re: Complex and Solve
  • From: Bob Hanlon <hanlonr357 at gmail.com>
  • Date: Fri, 24 Feb 2012 00:57:56 -0500 (EST)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com
  • References: <201202211115.GAA08330@smc.vnet.net>

Actually I should have checked, with version 8 Solve can handle
inequalities so either Reduce or Solve works here.

$Assumptions = rfe > 0 && l > 0;

r = 1;
\[Omega] = 300;
vrms = 2;
irms = 1/2;
\[Phi] = 30 Degree;

impedance = r + 1/(1/rfe + 1/(I \[Omega] l)) // FullSimplify;

voltage = vrms (Cos[\[Phi]] + I Sin[\[Phi]]) // Simplify;

Solve[{irms == voltage/impedance, $Assumptions}, {rfe,
    l}][[1]] // FullSimplify

{rfe -> (1/11)*(-7 + 30*Sqrt[3]), l -> (1/600)*(17 - 4*Sqrt[3])}

Alternatively,

Solve[{irms == voltage/impedance, Im[l] == 0, Im[rfe] == 0}, {rfe,
    l}][[1]] // FullSimplify

{rfe -> (1/11)*(-7 + 30*Sqrt[3]), l -> (1/600)*(17 - 4*Sqrt[3])}


Bob Hanlon

On Thu, Feb 23, 2012 at 5:46 AM,  <howard.lovatt at gmail.com> wrote:
> Thanks Bob,
>
> Your solution is much better than mine. I had no idea that Reduce could be used like you showed.
>
> Bizarre that Solve and Reduce behave so differently!
>
> Thanks again,
>
>  -- Howard.
>



--
Bob Hanlon



  • Prev by Date: Re: Reading Single and Double reals in Little-endian and Big-endian
  • Next by Date: Re: How best to implement a hash table in Mathematica
  • Previous by thread: Re: Complex and Solve
  • Next by thread: Re: Complex and Solve