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MathGroup Archive 2007

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Am I overlooking something?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg75089] Am I overlooking something?
  • From: jackgold at umich.edu
  • Date: Mon, 16 Apr 2007 20:17:06 -0400 (EDT)

Hi Folks,

I use DiscreteDelta in my work.  It is not, I assume, an oft used 
function but it does serve my purposes.  Now Attributes[DiscreteDelta] 
are "Orderless" and "Protected" but NOT "NumericFunction".  This 
puzzles me.  In seems to me that DiscreteDelta satisfies the first 
criterion in the following list.  The second item suggests that some 
functions which would ordinarily have the attribute NumericFunction 
have not been given this attribute intentionally!  The third item warns 
me about setting this attribute for DiscreteDelta - maybe. 
Incidentally, KroneckerDelta also does not have the NumericFunction 
attribute.

My question is, of course, why not? An oversight by Mathematica?

Here, for your convenience I copy the relevant items from the help menue.


◼ NumericFunction is an attribute that can be assigned to a 
symbol f to indicate that f[a, a, =85 ] should be considered a numeric 
quantity whenever all the a are numeric quantities.

◼ Most standard built‐in mathematical functions have the 
attribute NumericFunction.

◼ If you assign the attribute NumericFunction to a function that 
does not yield numerical values, then NumericQ will give misleading 
results.


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