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MathGroup Archive 2004

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Why does Mathematica 5.0 fail where Mathematica 4.1 works ?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg46996] Why does Mathematica 5.0 fail where Mathematica 4.1 works ?
  • From: Oleksandr Pavlyk <pavlyk at phys.psu.edu>
  • Date: Fri, 19 Mar 2004 01:35:49 -0500 (EST)
  • Organization: Penn State University; Department of Physics
  • Reply-to: pavlyk at phys.psu.edu
  • Sender: owner-wri-mathgroup at wolfram.com

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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