       Re: NSolve fails where Solve succeeds!

• To: mathgroup at smc.vnet.net
• Subject: [mg43500] Re: [mg43446] NSolve fails where Solve succeeds!
• From: Michael Schreiber <michaelschreiber at mac.com>
• Date: Thu, 18 Sep 2003 05:39:12 -0400 (EDT)
• Sender: owner-wri-mathgroup at wolfram.com

```On Wednesday, Sep 17, 2003, at 13:59 Europe/Vienna, Pavel Pokorny wrote:

>
>   Dear Mathematica friends
>
>    Solve[{{a,b},{c,d}}==0]

What is the correct solution? Is it a trivial problem:

In:=
Solve[a\[Equal]0&&b\[Equal]0&&c\[Equal]0&&d\[Equal]0]

Out=
{{a\[Rule]0,b\[Rule]0,c\[Rule]0,d\[Rule]0}}

Or is it the short notation for a system of equations (Mathematica Book
3.4.4):

In:=
Reduce[{a x+b y,c x+d y}\[Equal]0]

Out=
\!\(y \[Equal] 0 && x \[Equal] 0 || x ¡Á 0 && c \[Equal] \(-\(\(d\ y\)\/
x\)\) && a \[Equal] \(-\(\(b\ y\)\/x\)\) ||
x \[Equal] 0 && y ¡Á 0 && d \[Equal] 0 && b \[Equal] 0\)

>
> gives the correct solution in Mathematica 5.0 while
>
>    NSolve[{{a,b},{c,d}}==0]
>
> fails.

It does not fail but returns:

From In:=
\!\(\*
RowBox[{\(Solve::"elist"\), \(\(:\)\(\ \)\), "\<\"List encountered
during logical expansion
of \\!\\({a, b}\\). \\!\\(\\*ButtonBox[\\\"More¡¦\\\", \
ButtonData:>\\\"Solve::elist\\\"]\\)\"\>"}]\)

Out=
NSolve[{{a,b},{c,d}}\[Equal]0]

The error code ::elist is explained if you click
->
ore
->
Generated when the internalLogicalExpandfunction encounters a list
rather a \
combination of equations and logical functions.

>
> Is it a bug or an intention?
>
> It would be nice to have Solve and NSolve giving
> as close results as possible.
>
> --
> Pavel Pokorny
> Math Dept, Prague Institute of Chemical Technology
> http://www.vscht.cz/mat/Pavel.Pokorny
>
>
F Schreiber
Heimscholleg 26 Wien, A1130 Austria Europe
ichael at Schreiber.at

```

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