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MathGroup Archive 2004

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Reduce

  • To: mathgroup at smc.vnet.net
  • Subject: [mg46879] Reduce
  • From: "Tony Harker" <a.harker at ucl.ac.uk>
  • Date: Fri, 12 Mar 2004 23:39:25 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

  I find Reduce in version 5 seems to have lost some functionality. In
version 4 the input

form = Reduce[{A Exp[? y] ==
     B Cos[? y] + C Sin[? y] /.
          y -> -a/2, D Exp[-? y] == B Cos[? y] + C Sin[? y] /.
        y -> a/2, (D[A Exp[? y],
      y] == D[(B Cos[? y] + C Sin[?
          y]), y]) /. y -> -a/2, (D[D Exp[-? y], y] == D[(B Cos[
        ? y] + C Sin[? y]), y]) /. y -> a/2}, {A, B, C, D}]

 produces a perfectly sensible result starting

A == 0 && D == 0 || A == B && D == B && ? == 0 && ? == 0....

 In version 5 the same input causes a long period of cogitation (far longer
than version 4 took to produce its result), and finally emerges with a
suggestion that I should look for further information on its failure which
is not yet there.

  Mathematically, the problem is relatively straightforward: the equations
reduce to M x = 0,where x={A,B,C,D}, so we just need the conditions under
which the determinant of M is zero, and any other special cases.

  Are there new controls for Reduce in version 5 which will allow its
functionality to be recovered, or is it irrevocably broken?


Tony Harker

----------------------------------------
 Dr A.H. Harker
 Director of Postgraduate Studies
 Deputy Head, Condensed Matter and Materials Physics Group
 Department of Physics and Astronomy
 University College London
 Gower Street
 LONDON
 WC1E  6BT
 (44)(0)207 679 3404
 a.harker at ucl.ac.uk


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