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Re: How to require integer subscripts to match a simple pattern

• To: mathgroup at smc.vnet.net
• Subject: [mg111544] Re: How to require integer subscripts to match a simple pattern
• From: Peter Pein <petsie at dordos.net>
• Date: Wed, 4 Aug 2010 07:39:48 -0400 (EDT)
• References: <i3bd4l$pg1$1@smc.vnet.net>

Am Wed, 4 Aug 2010 09:50:13 +0000 (UTC)
schrieb Tom D <tomdickens at att.net>:

> I am trying to create an indexed function that would be of the form
> 
> M_(j,,j+1) [a,b] := func(j,a,b) ,
> 
> where M has the two subscripts j and j+1, i. e. I need the 2nd
> subscript to match only when it is 1 more than the first.
> 
> I know how to do this if I made the argument 'j' a normal argument,
> that is, not a subscript. (Use the /; operator.)
> 
> How can I do this for the subscripts?
> 
> (These are propagator matrices that either go one level up, or one
> down, so I'll have two M's, a (j, j+1) and a (j,,j-1) version.)
> 
> Thanks,
> 
> Tom
> 

Hi Tom,

this works similar to the definition of a function:

In[7]:= Clear[M]
Subscript[M, j_, j_ + 1][a_, b_] := func[j, a, b]

In[9]:= Subscript[M, 5, 6][x, y]

Out[9]= func[j, x, y]

In[10]:= Subscript[M, 6, 5][p, q]

Out[10]= Subscript[M, 6, 5][p, q]

hth,
Peter