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Re: Subscript on plus expression

  • To: mathgroup at smc.vnet.net
  • Subject: [mg128713] Re: Subscript on plus expression
  • From: "Dave Snead" <dsnead6 at charter.net>
  • Date: Mon, 19 Nov 2012 04:10:17 -0500 (EST)
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  • References: <20121117084935.868E56AF3@smc.vnet.net> <k8a898$89n$1@smc.vnet.net> <20121118221341.5BC226958@smc.vnet.net>

Nasser --,

I'm using these as tensor indices.

Although Bob Hanlon offered a workaround (thanks Bob)
Format[Subscript[arg_Plus, k_]] :=
Subscript["(" <> StringJoin @@
    Riffle[ToString /@ (List @@ arg),
     " + "] <> ")", k]
Subscript[a + b + 2, k],

I think the folks at Mathematica should fix this and insert the parentheses.
The output of Subscript[Plus[a,b],k] should not be represented as 
Plus[a,Subscript[b,k]]!

-- Dave

-----Original Message----- 
From: Nasser M. Abbasi
Sent: Sunday, November 18, 2012 2:13 PM
To: mathgroup at smc.vnet.net
Subject: [mg128713] Re: Subscript on plus expression

On 11/18/2012 3:03 AM, Dave Snead wrote:
> Hi,
>
> Mathematica fails to parenthesize the a+b in
> Subscript[Plus[a,b],k]
>
> so the output looks identical to
> Plus[a,Subscript[b,k]]
>
> Is this a bug?
> Is there an option to force the parentheses?
>
> Thanks in advance,
> Dave Snead
>
>
>

Actually, just typing

(a+b)
     k

and then hitting ENTER will result in

a+b
    k

i.e. the () are gone. Same effect you showed.

It might be because subscript are meant to be applied to an atomic symbol
and not combined expression like a+b. I do not know.  I am not even sure
what (a+b)_k is supposed to mean, math wise. Is this meant to
be on the code or in a text cell? If it is in the code itself,
how will it be used?

--Nasser







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