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Re: Product over an arbitrary index.
*To*: mathgroup at smc.vnet.net
*Subject*: [mg68692] Re: [mg68683] Product over an arbitrary index.
*From*: Sseziwa Mukasa <mukasa at jeol.com>
*Date*: Thu, 17 Aug 2006 04:17:51 -0400 (EDT)
*References*: <200608160736.DAA06150@smc.vnet.net>
*Sender*: owner-wri-mathgroup at wolfram.com
On Aug 16, 2006, at 3:36 AM, quantieny at gmail.com wrote:
> I have a function f(x,y) that I would like to compute the product
> over indices i,j
> where i goes from an arbitrary list {1,4,3} and j goes 1 to m.
This statement is a little unclear, are you taking the product f[i,j]
where i is the sequence {1,4,3}, j is 1..m?
The way to do this in Mathematica is to store the sequence for i in a
list and use the index of the iterator in product to get the
appropriate sequence element. If your sequence is very long but you
have a generating function, just pass the index to the generating
function.
> Is this possible in mathematica the function Product itself seems to
> only work over a continous sequence and it is not clear how I can use
> two set of indices.
You can specify as many indices as you want for example
iSequence={1,4,3};
m=50;
Product[f[iSequence[[i]],j],{i,Length[iSequence]},{j,m}]
> Additionally can I specify the product over an intersection or
> complement of a list?.
Using the technique above you can do pretty much anything you want,
all you need is a function that maps an index to a sequence value.
Regards,
Ssezi
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