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Re: What is f[1]? Advanced question

  • To: mathgroup at smc.vnet.net
  • Subject: [mg131367] Re: What is f[1]? Advanced question
  • From: Helen Read <readhpr at gmail.com>
  • Date: Mon, 1 Jul 2013 05:51:38 -0400 (EDT)
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  • References: <kqm704$hpb$1@smc.vnet.net>

x is not an array. It is a symbol which in this case has not been 
defined. It does not refer to the list.

If you were to name the array, like this:

b= Array[x, 3]

The list is named b, and you can extract the entries with double brackets.

b[[2]]

Perhaps your confusion arises from the fact that b[[2]] and x[2] are 
equal. Here is another example that will perhaps clarify.

c = Array[x, 5, -8]

c[[1]]  (* first entry of c. Not the same as x[1] *)

c[[2]]  (* second entry of c. Not the same as x[2] *)






On 6/29/2013 4:48 AM, Tomas Garza wrote:
> In[2]:= Array[x, 3]
>
> Out[2]= {x[1], x[2], x[3]}
>
> x is an array and is indexed with single brackets (cf. the Help browser).
> -Tomas
>
>> From: talmanl at gmail.com
>> Subject: Re: What is f[1]? Advanced question
>> To: mathgroup at smc.vnet.net
>> Date: Fri, 28 Jun 2013 04:15:13 -0400
>>
>> On Tue, 25 Jun 2013 19:14:08 -0600, 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
>>
>> x most certainly *is* a function.  Its a function whose domain contains
>> just the three numbers 1, 2, and 3.
>>
>> And it is *not* an array.  Mathematica has lists, which it uses as arrays
>> on occasion. An array, y, is indexed with double brackets:  a[[1]],
>> a[[2]], etc.
>>
>> --Louis A. Talman
>>     Department of Mathematical and Computer Sciences
>>     Metropolitan State University of Denver
>>
>>     <http://rowdy.msudenver.edu/~talmanl>
>   		 	   		
>






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