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MathGroup Archive 2004

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Re: Why does Mathematica 5.0 fail where Mathematica 4.1 works ?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg47022] Re: Why does Mathematica 5.0 fail where Mathematica 4.1 works ?
  • From: drbob at bigfoot.com (Bobby R. Treat)
  • Date: Sat, 20 Mar 2004 03:50:34 -0500 (EST)
  • References: <c3e5b5$qm1$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

y isn't "an unknown variable," of course. YOU introduced the variable,
and didn't tell Solve to eliminate it... so it didn't. (It can't, in
this case, but that's another matter entirely.)

You wanted y==E, so make the substitution y->E and you'll have the
same answer as in version 4.1.

Bobby

Oleksandr Pavlyk <pavlyk at phys.psu.edu> wrote in message news:<c3e5b5$qm1$1 at smc.vnet.net>...
> Hi,
> 
> I was looking at excellent talk by Daniel Lichtblau
> "Tactics for solving equations in Mathematica" from
> 
> http://library.wolfram.com/infocenter/Conferences/337/
> 
> In the "Tricky Solve problem" chapter we find the
> following
> 
>    k = E;
>    Solve[ { y == x^y , y == k }, x ]
> 
> So here are outputs in the freshly started notebooks in
> two versions of Mathematica
> 
> Mathematica 4.1 on Solaris returns
> 
>       E^(1/E)
> 
> and Mathematica 5.0 on Windows returns
> 
>       (1/y)^(-1/y)
> 
> where y is an unknown variable.
> 
> Both versions complain that inverse functions were used and hence
> some solution maybe lost. See output from 5.0 attached below.
> 
> I would not be surprised of somebody tells me this bug has been fixed
> in 5.0.1. In fact this is what happened with all earlier bug reports
> posted on this mailing list.
> 
> I must ask our sysadmin if our departmental subscription
> qualifies for a free upgrade to Mathematica 5.0.1. ;)
> 
> I can't help but feel that Mathematica should provide bug
> (not limitation) fixing patches for Mathematica users free
> of charge. But that's me...
> 
> Sasha
> 
> In[1]:=
> $Version
> 
> Out[1]=
> 5.0 for Microsoft Windows (June 11, 2003)
> 
> In[2]:=
> sol = x /. First[Solve[{y == x^y, y == E}, x]]
> 
>  From In[2]:=
> \!\(\*
>    RowBox[{\(Solve::"ifun"\), \(\(:\)\(\ \)\), "\<\"Inverse functions are
>        being used by \\!\\(
>        Solve\\), so some solutions may not be found; use Reduce for 
> complete \
> solution information. \\!\\(\\*ButtonBox[\\\"More?\\\", \
> ButtonStyle->\\\"RefGuideLinkText\\\", ButtonFrame->None, \
> ButtonData:>\\\"Solve::ifun\\\"]\\)\"\>"}]\)
> 
> Out[2]=
> \!\(\((1\/y)\)\^\(\(-1\)/y\)\)


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