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Re: What is f[1]? Advanced question

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  • Subject: [mg131309] Re: What is f[1]? Advanced question
  • From: Bob Hanlon <hanlonr357 at gmail.com>
  • Date: Wed, 26 Jun 2013 01:04:31 -0400 (EDT)
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  • References: <20130626011408.DC7E86A2B@smc.vnet.net>

Do[x[i] = i/10., {i, 1, 3}]


x is a user-defined function whose domain is just the integers 1, 2, and
3.  Like all functions, its Head is Symbol.


Head /@ {x, Exp, Mean}


{Symbol, Symbol, Symbol}


The function definitions are stored in the DownValues of the symbol


DownValues[x]


{HoldPattern[x[1]] :> 0.1, HoldPattern[x[2]] :> 0.2, HoldPattern[x[3]] :>
0.3}


Like any function, when given an argument outside of its defined domain, it
returns unevaluated.


x[4]


x[4]



Bob Hanlon




On Tue, Jun 25, 2013 at 9:14 PM, amannucci
<Anthony.J.Mannucci at jpl.nasa.gov>wrote:

> I have found a Mathematica program with the following construct:
> x[1]=0.1
> x[2]=0.2
> x[3]=0.3
>
> or
> Do[x[i]=i/10.,{i,1,3}]
>
> x is not a function. It is not a list. What is it? If I query x thus:
> ?x
>
> the answer is just what I have written above. Mathematica knows about
> x[1], x[2], etc. How does Mathematica know about the "elements" of x?
>
> In some other sense, I could have written:
> y1 = 0.1
> y2 = 0.2
> y3 = 0.3
>
> But
> ?y
>
> obviously gives a different result (just returns y).
>
> Thank you.
>
>




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