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Re: why no result & no error from this recursion

  • To: mathgroup at smc.vnet.net
  • Subject: [mg82510] Re: why no result & no error from this recursion
  • From: David Bailey <dave at Remove_Thisdbailey.co.uk>
  • Date: Tue, 23 Oct 2007 05:27:53 -0400 (EDT)
  • References: <200710190904.FAA05304@smc.vnet.net> <DB2B10DE-2D39-482A-ACA4-6DDB5CECB1E4@jeol.com> <ffcjkc$sbg$1@smc.vnet.net>

Murray Eisenberg wrote:
> When the evaluation ended (very quickly, and with no result), the front 
> end was immediately ready for the next input I typed.
> 
> Sseziwa Mukasa wrote:
>> On Oct 19, 2007, at 5:04 AM, Murray Eisenberg wrote:
>>
>>> Why does the following recursion produce neither a result nor an error
>>> message -- nor a system crash?
>>>
>>> Block[{$RecursionLimit=50002}, (If[#<1, "", "." <> #0[# - 1]] &)[50000]]
>>>
>>> I even tried setting $RecursionLimit=Infinity, but no change.
>>>
>>> I presume this is just bumping up against a hardware/OS limit, so I'm
>>> surprised to get no error message and no crash.
>> My guess is that the front end is having problems formatting 50000 '.' 
>> for display.  I've noticed sometimes that calculations that generate 
>> long strings on output can appear to have hung but the kernel has not 
>> crashed and the front end is unresponsive.
>>
>> Regards,
>>
>> Ssezi
>>
> 
Hi Murray,

No it can't be the front end, because this blows up too:

f[Block[{$RecursionLimit =
      50002}, (If[# < 1, "", "." <> #0[# - 1]] &)[43621]];]

Note that 43620 is the highest argument that works as expected.

David Bailey
http://www.dbaileyconsultancy.co.uk


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