Re: product formula in mathematica

*To*: mathgroup at smc.vnet.net*Subject*: [mg68767] Re: [mg68702] product formula in mathematica*From*: Murray Eisenberg <murray at math.umass.edu>*Date*: Fri, 18 Aug 2006 03:12:13 -0400 (EDT)*Organization*: Mathematics & Statistics, Univ. of Mass./Amherst*References*: <200608170818.EAA24861@smc.vnet.net>*Reply-to*: murray at math.umass.edu*Sender*: owner-wri-mathgroup at wolfram.com

In general, if you have a list lis of numbers, you can find their product by Apply[Times, lis] or, in abbreviated format: Times @@ lis So a strategy would be to form first the list of numbers to be multiplies, and then use the above. Now I'm not quite sure what you mean by x_i in your posting. Are you trying to explicitly use subscripts (via the Notation package)? Indices via the x[[i]] notation? Ordinary arguments via the x[i] notation. In any case, since you have no particular pattern in mind for the subscripts, you'll somehow have to specify them one-by-one. For example (doing it slowly, step by step): x = Table[i^2, {i, 1, 10}] {1, 4, 9, 16, 25, 36, 49, 64, 81, 100} indices = {1,3,4,9} {1, 3, 4, 9} x[[indices]] {1, 9, 16, 81} f[x_] := 1/x (* for example *) f[x[[indices]]] {1, 1/9, 1/16, 1/81} Times @@ f[x[[indices]]] 1/11664 In the above, I'm using, and assuming you have, a function f that has attribute Listable. (Also, I actually showed the InputForm of the two results that have fractions in them.) frou wrote: > Hi I am interested in doing a product over a set of indices that are > not continuous > Product [ f(x_i) , { x_i, 1,3,4,9}] Is this possible it appears > that the iterator wouldonly take sequences such as 1...10 etc. > > Thanks > > -- Murray Eisenberg murray at math.umass.edu Mathematics & Statistics Dept. Lederle Graduate Research Tower phone 413 549-1020 (H) University of Massachusetts 413 545-2859 (W) 710 North Pleasant Street fax 413 545-1801 Amherst, MA 01003-9305

**References**:**product formula in mathematica***From:*"frou" <quantieny@gmail.com>