Re: Replacements in NonCommutativeMultiply

• To: mathgroup at smc.vnet.net
• Subject: [mg72560] Re: [mg72558] Replacements in NonCommutativeMultiply
• From: "Chris Chiasson" <chris at chiasson.name>
• Date: Tue, 9 Jan 2007 07:17:21 -0500 (EST)
• References: <200701081000.FAA14451@smc.vnet.net>

```It appears to be due to the Flat attribute of NonCommutativeMultiply.
You can always use Verbatim[NonCommutativeMultiply[]] -> 1

On 1/8/07, David Park <djmp at earthlink.net> wrote:
> Can anyone explain the following result?
>
> Times[a, NonCommutativeMultiply[], NonCommutativeMultiply[i, c]];
> % /. NonCommutativeMultiply[] -> 1 // FullForm
>
> giving
>
> Times[a, NonCommutativeMultiply[1, i, c]]
>
> I believe the result should be
>
> Times[a, NonCommutativeMultiply[i, c]]
>
> The reason I get an empty argument sequence is that the factors contain 'scalars' and 'vectors' and the scalars get factored out. Only the vector part is noncommutative.
>
> The result Mathematica gives is definitely a problem because when the 1 is factored out again to simplify we arrive back at the starting point.
>
> A similar replacement is done with CircleDot works properly.
>
> Times[a, CircleDot[], CircleDot[i, c]];
> % /. CircleDot[] -> 1 // FullForm
>
> Times[a, CircleDot[i, c]]
>
> David Park
> djmp at earthlink.net
>
>
>

--
http://chris.chiasson.name/

```

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