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MathGroup Archive 2003

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Re: Solve bug in Mathematica 5

  • To: mathgroup at smc.vnet.net
  • Subject: [mg44021] Re: [mg44010] Solve bug in Mathematica 5
  • From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
  • Date: Sat, 18 Oct 2003 03:12:14 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

On Friday, October 17, 2003, at 06:14 PM, Artūras Acus wrote:

> Hi,
>
> The following example demonstrates Mathematica 5.0 "improvements"
> in Solve.
>
> lygtys2={E^(a*k*Cot[a*k])*Subscript[A, 1] - Cos[a*k]*Subscript[A, 2] +
> Sin[a*k]*Subscript[B, 2] == 0,
>  -(E^(a*k*Cot[a*k])*k*Cot[a*k]*Subscript[A, 1]) -
> k*Sin[a*k]*Subscript[A, 2] -
>    k*Cos[a*k]*Subscript[B, 2] == 0, Cos[a*k]*Subscript[A, 2] +
> Sin[a*k]*Subscript[B, 2] -
>    E^(a*k*Cot[a*k])*Subscript[B, 3] == 0,
>  -(k*Sin[a*k]*Subscript[A, 2]) + k*Cos[a*k]*Subscript[B, 2] -
>    E^(a*k*Cot[a*k])*k*Cot[a*k]*Subscript[B, 3] == 0}
>
> Solve[lygtys2, {Subscript[A, 2], Subscript[B, 2], Subscript[B, 3],
> Subscript[A, 1]}]
>
> gives {0,0,0,0}, thought equations are lineary dependent. 4.1 returns
> correct rezult.
>
>
>

If you want to see the real improvement,  look at the answer you get 
with Reduce in v. 5 and compare it with the one version 4 returns.
  I agree that Solve in v.5  should do a little better with this example 
but actually it will give you the solution you want if you use the 
Rational mode instead of the default Generic:

Solve[lygtys2, {Subscript[A, 2], Subscript[B, 2],
    Subscript[B, 3], Subscript[A, 1]}, Mode -> Rational]

(long output suppressed).

Andrzej Kozlowski
Yokohama, Japan
http://www.mimuw.edu.pl/~akoz/
http://platon.c.u-tokyo.ac.jp/andrzej/


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