       Re: What is f? Advanced question

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• Subject: [mg131309] Re: What is f? 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.

{Symbol, Symbol, Symbol}

The function definitions are stored in the DownValues of the symbol

DownValues[x]

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

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

x

x

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=0.1
> x=0.2
> x=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, x, 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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