Mathematica 9 is now available
Services & Resources / Wolfram Forums
-----
 /
MathGroup Archive
2006
*January
*February
*March
*April
*May
*June
*July
*August
*September
*October
*November
*December
*Archive Index
*Ask about this page
*Print this page
*Give us feedback
*Sign up for the Wolfram Insider

MathGroup Archive 2006

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

Search the Archive

solving with inverse functions/inexact coefficients

  • To: mathgroup at smc.vnet.net
  • Subject: [mg67397] solving with inverse functions/inexact coefficients
  • From: Dave Spence <dspence at ics.mq.edu.au>
  • Date: Wed, 21 Jun 2006 02:13:39 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

I'm trying to solve a set of simultaneous equations describing a laser cavity. A much simplified set of equations in Real unknowns F1, F2 and NU looks like this:

F2  == Exp[0.76 NU] F1, F1 == 0.5 F2 Exp[0.76 NU], 0.5 F2 + NU == 15

They can be solved by hand very easily with two solutions, {F1=F2=0 && NU = 15} and {NU=0.46, F1=14.5,  F2=29.1}

Now Solve cannot solve these equations unless I change both instances of 0.76 to integers. Reduce seems to hang (or at least take too long to return and answer). Reduce can solve the problem quickly if I change both instances of 0.76 to 0.75! Reduce gives the message "Reduce::ratnz: Reduce was unable to solve the system with inexact coefficients. The answer was obtained by solving a corresponding exact system and numericizing the result"

I guess this is just a difficulty with the way mathematica attempts to solve problem. There are references in the manuals to difficulties solving multiple simultaneous equations that all invoke inverse functions. Are there any options I can set to enable mathematica to quickly solve these equations?

I note that while these equations can be manipulated by hand into a form that can be solved by mathematica, by full set of equations are far more complex and can't easily be edited by hand.


  • Prev by Date: preclude mathematical meaning of OverBar etc
  • Next by Date: Re: Interrogating lists of unequal lenghths
  • Previous by thread: preclude mathematical meaning of OverBar etc
  • Next by thread: Re: solving with inverse functions/inexact coefficients