RE: NSolve fails where Solve succeeds!

• To: mathgroup at smc.vnet.net
• Subject: [mg43488] RE: [mg43446] NSolve fails where Solve succeeds!
• From: "David Park" <djmp at earthlink.net>
• Date: Thu, 18 Sep 2003 05:38:51 -0400 (EDT)
• Sender: owner-wri-mathgroup at wolfram.com

```Pavel,

The Solve documentation says:

Simultaneous equations can be combined either in a list or with &&.

So it is not clear to me why

Solve[{{a, b}, {c, d}} == 0]

even works. It is clearly not a correct equation unless some
"interpretation" is done. (You can't just simply Thread it either.) How can
an array be equal to a single number? I think this would have to be
considered an undocumented feature.

The following would be a more correct equation and it also works.

Solve[{{a, b}, {c, d}} == Array[0 &, {2, 2}]]

In the Examples they do have a case of the following form:

Solve[{a, b, c, d} == 0]

and

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

also works.

I would agree that this is an area of confusion. Also in DSolve and NDSolve.
The documentation should be more clear as to when Threading and
"interpretation" are performed on the input equations and NSolve and Solve
could be more consistent.

David Park

-----Original Message-----
From: Pavel Pokorny [mailto:Pavel.Pokorny at vscht.cz]
To: mathgroup at smc.vnet.net
Subject: [mg43488] [mg43446] NSolve fails where Solve succeeds!

Dear Mathematica friends

Solve[{{a,b},{c,d}}==0]

gives the correct solution in Mathematica 5.0 while

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

fails.

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

```

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