Re: RE: Re: User problem

*To*: mathgroup at smc.vnet.net*Subject*: [mg24079] Re: [mg24023] RE: [mg23997] Re: [mg23971] User problem*From*: john.tanner at baesystems.com*Date*: Fri, 23 Jun 2000 02:26:46 -0400 (EDT)*Sender*: owner-wri-mathgroup at wolfram.com

The "Magic Number" coincides with the point where Table starts to produce PackedArrays: In[1]:= Developer`PackedArrayQ[Table[i, {i, 249}]] Out[1]:= False In[2]:= Developer`PackedArrayQ[Table[i, {i, 250}]] Out[2]:= True This break point of 250 seems to be for the total number of index entries in the Table, thus a multi-dimensional Table has a break point at (e.g.) Table[{i,j}, {i, 5},{j, 50}]. I cannot find a reference to this in the documentation, but I appreciate there should be such a break point even if I would like some control over it! This sometimes has implications for expressions which are tested at a small number of points and then used with a larger number: it is wise to check with different Table sizes if you suspect the behaviour would change. PackedArrays are extremely useful, and their near-seamless incorporation into Mathematica is a real joy, but they do behave differently in some circumstances even in "legal" code. It is interesting, but not surprising given the output is in a different form, to note this difference in "illegal" code. hwolf (hwolf at debis.com@SMTP at MSMR02) writes: > >Notwithstanding the original code being illegal, 250 appears as a >magic number. Compare: > >In[2]:= Table[i = i + 1, {i, 249}] > >In[3]:= Table[i = i + 1, {i, 250}] > >-- Hartmut > >> -----Original Message----- >> From: BobHanlon at aol.com [SMTP:BobHanlon at aol.com] To: mathgroup at smc.vnet.net >To: mathgroup at smc.vnet.net >> Sent: Monday, June 19, 2000 7:46 AM >> To: mathgroup at smc.vnet.net >> Subject: [mg23997] Re: [mg23971] User problem >> >> >> In a message dated 6/18/2000 3:39:33 AM, joseph468 at yahoo.com >> writes: >> >> >I am trying to contstruct a table of random integers >> >between 1 and 4. I'd like to vary the number of >> >elements in the table from time to time. The >> >contruction that I use in Mathematica is as follows: >> > >> >genome = Table[i = Random[Integer, {1, 4}], {i, 249}] >> > >> >The problem with this is as follows: the above >> >generates tables of varying length up to and including >> >249 elements. However, when I try to generate any >> >table containing more than 249 elements, I get the >> >following error message on my screen: >> > >> >This program has performed an illegal operation and >> >will be shut down. If the problem persists please >> >contact the vendor. >> > >> >I have version 4 of Mathematica, and am running it on >> >a Windows98 platform (Dell NoteBook) >> > >> >> genome = Table[Random[Integer, {1, 4}], {249}]; >> >> >> Bob Hanlon