Re: understanding code

*To*: mathgroup at smc.vnet.net*Subject*: [mg114220] Re: understanding code*From*: Leonid Shifrin <lshifr at gmail.com>*Date*: Sat, 27 Nov 2010 03:38:32 -0500 (EST)

Sorry, I meant PostIncrement (although similar arguments should apply to PreIncrement as well) On Fri, Nov 26, 2010 at 1:26 PM, Bill Rowe <readnews at sbcglobal.net> wrote: > On 11/25/10 at 5:57 AM, sam.takoy at yahoo.com (Sam Takoy) wrote: > > >The following code: > > >i[_] = 0; > >i[1]++ > >i[1]++ > >i[1]++ > >i[1]++ > > >return 0 1 2 3 4. I'd like to understand whats going on here. That > >is, > > >What is i? Is it a function? And what is i[1]? Is it a function or > >a value? Etc... > > It is a function. i[1] is the function i evaluated at i. You can > see what is going on by using Trace, i.e., > > In[3]:= Trace[i[1]++] > > Out[3]= {i(1)++,{i(1),0},{i(1)=1,1},0} > > As you can see, i[1] gets evaluated to whatever value it had > previously which initially is zero. Then the result gets > incremented by 1 and is then assigned to be the new value for > i[1]. This last step is not something I would have expected > without your example and I don't know why it occurs. > > I can see times where this behavior might be useful. For > example, it is at times convenient to see i[1] as a subscripted > variable. Thinking of i[1] this way, the notation i[1]++ would > be interpreted as incrementing the subscripted variable by one > and the Mathematica behavior is consistent with this. > > >

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