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MathGroup Archive 2006

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Re: Product and Summation sign

  • To: mathgroup at smc.vnet.net
  • Subject: [mg66844] Re: Product and Summation sign
  • From: Bill Rowe <readnewsciv at earthlink.net>
  • Date: Thu, 1 Jun 2006 06:54:58 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

On 5/31/06 at 6:31 AM, actuary at mchsi.com wrote:

>The "HoldForm" suggestion works.

>My question came about because I recently purchased "MathStatica"
>and was working through the material on Maximum Likehood Estimate. 
>The examples contained in the test provided output from inputs that
>constructed a likelihood function that contained the product sign,
>just like one would write it out if doing by paper and pencil. 
>Through the use of function "SuperLog", the Log of the likelihood
>function would be presented with a summation sign.

>None of the examples used "HoldForm".  My first thought was that a
>Mathematica setting was not set correctly (StandardForm not
>checked--It was)and that was the reason my output looked different
>than that in the text.

>Any comments would be appreciated.

It is true the examples given with MathStatica do not use Hold or HoldForm. The reason these examples work in that manner is the number of things to sum or multiply is given as a variable that has not been defined. That is if you are using TraditionalForm or StandardForm as you default output format, the result of

Sum[Log[Subscript[x, i]], {i, 1, n}]

will appear with the summation sign.

The only thing SuperLog does is convert the logarithm of a product to the sum of logarithms. It does not alter the way Mathematica evaluates arguments to either Sum or Product. Of course, I am making this claim based on the behavior of MathStatica code since I cannot inspect the actual code used.
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