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Re: Re: simple nest

  • To: mathgroup at smc.vnet.net
  • Subject: [mg106740] Re: [mg106676] Re: [mg106661] simple nest
  • From: DrMajorBob <btreat1 at austin.rr.com>
  • Date: Fri, 22 Jan 2010 05:39:01 -0500 (EST)
  • References: <201001201150.GAA09275@smc.vnet.net>
  • Reply-to: drmajorbob at yahoo.com

How about

Clear[func,func2, test]
func[x_, y_, z_, p_, q_] := IntegerPart[{z, p, q}^0.9]
func2[x_, y_][{z_, p_, q_}] := func[x, y, z, p, q]
test[{_, a_, _}, {_, b_, _}] := UnsameQ[a, b]
NestWhileList[func2[1, 2], {1, 100, 1000}, test, 2]

{{1, 100, 1000}, {1, 63, 501}, {1, 41, 269}, {1, 28, 153}, {1, 20,
   92}, {1, 14, 58}, {1, 10, 38}, {1, 7, 26}, {1, 5, 18}, {1, 4,
   13}, {1, 3, 10}, {1, 2, 7}, {1, 1, 5}, {1, 1, 4}}

or

Clear[func3, test]
func3[{z_, p_, q_}] := IntegerPart[{z, p, q}^0.9]
test[{_, a_, _}, {_, b_, _}] := UnsameQ[a, b]
NestWhileList[func3, {1, 100, 1000}, test, 2]

{{1, 100, 1000}, {1, 63, 501}, {1, 41, 269}, {1, 28, 153}, {1, 20,
   92}, {1, 14, 58}, {1, 10, 38}, {1, 7, 26}, {1, 5, 18}, {1, 4,
   13}, {1, 3, 10}, {1, 2, 7}, {1, 1, 5}, {1, 1, 4}}

Bobby

On Thu, 21 Jan 2010 03:50:03 -0600, Leonid Shifrin <lshifr at gmail.com>  
wrote:

> Hi Francisco,
>
> When you use NestWhile and wish to access several past results, they  
> should
> correspond to different arguments of your test function.
>
> Here is some specific function:
>
> Clear[func];
> func[x_, y_, z_, p_, q_] := IntegerPart[{z, p, q}^0.9]
>
> Here is how we can use it to achieve what you want:
>
> In[2]:= NestWhileList[
>  func[1, 2, #[[1]], #[[2]], #[[3]]] &, {1, 100, 1000},
>  UnsameQ[#1[[2]], #2[[2]]] &, 2]
>
> Out[2]= {{1, 100, 1000}, {1, 63, 501}, {1, 41, 269}, {1, 28,
>   153}, {1, 20, 92}, {1, 14, 58}, {1, 10, 38}, {1, 7, 26}, {1, 5,
>   18}, {1, 4, 13}, {1, 3, 10}, {1, 2, 7}, {1, 1, 5}, {1, 1, 4}}
>
> I used NestWhileList to make it more transparent what's going on. Or, in
> this case, it may be less confusing to use pure function with named
> arguments for the test:
>
> In[3]:= NestWhileList[
>  func[1, 2, #[[1]], #[[2]], #[[3]]] &, {1, 100, 1000},
>  Function[{this, prev}, UnsameQ[this[[2]], prev[[2]]]], 2]
>
> Out[3]= {{1, 100, 1000}, {1, 63, 501}, {1, 41, 269}, {1, 28,
>   153}, {1, 20, 92}, {1, 14, 58}, {1, 10, 38}, {1, 7, 26}, {1, 5,
>   18}, {1, 4, 13}, {1, 3, 10}, {1, 2, 7}, {1, 1, 5}, {1, 1, 4}}
>
> Note that the first argument is the "oldest" result and the last  
> argument is
> the most recent one, and the total number of arguments to the test  
> function
> is regulated by the fourth parameter to NestWhile(List) - 2 in our case.
> Note also that pure functions silently ignore excessive arguments passed  
> to
> them. These two facts imply that you may get obscure mistakes if you  
> specify
> the wrong (too large) number of most recent results *and* use a pure
> function for testing.
>
> Hope this helps.
>
> Regards,
> Leonid
>
>
> On Wed, Jan 20, 2010 at 2:50 PM, Francisco Gutierrez  
> <fgutiers2002 at yahoo.com
>> wrote:
>
>> Dear group:
>> I have a function that gets five arguments, two of which are fixed, and
>> three vary. Its output are three numbers. So it can be nested, for  
>> example
>> over some initial values.
>> Say:
>> Nest[func[arg1,arg2,#[[1]],#[[2]],#[[3]]]&,{init1,init2,init3},k]
>>
>> Simple enough, works well.
>> Now I want to nest the same function, while the second non fixed  
>> argument
>> changes at each step. I thought the "natural" way of doing this was:
>>
>> NestWhile[func[arg1,arg2,#[[1]],#[[2]],#[[3]]]&,{init1,init2,init3},UnsameQ[#[[2]]&,2],
>> but this evidently does not work.
>>
>> So: in a NestWhile how do I create tests over parts of the outputs of a
>> function?
>> Thanks!
>> Fg
>>
>>


-- 
DrMajorBob at yahoo.com


  • References:
    • simple nest
      • From: Francisco Gutierrez <fgutiers2002@yahoo.com>
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