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Re: Manually nested Tables faster than builtin nesting?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg113434] Re: Manually nested Tables faster than builtin nesting?
  • From: Sebastian Schmitt <sschmitt at physi.uni-heidelberg.de>
  • Date: Thu, 28 Oct 2010 04:28:18 -0400 (EDT)

Hi Tomas!

With "manually" I mean

"Table[Table[..., {i, imax}], {j, jmax}]"

(two Tables explicitly/manually)

instead of

"Table[..., {i, imax}, {j, jmax}]"

(one Table but two iterators).

Can you explain the difference in speed?

Cheers,

Sebastian

PS:

$Version
"7.0 for Linux x86 (64-bit) (February 18, 2009)"

$ grep "model name" /proc/cpuinfo

model name      : Intel(R) Core(TM)2 Duo CPU     P8600  @ 2.40GHz
model name      : Intel(R) Core(TM)2 Duo CPU     P8600  @ 2.40GHz

Tomas Garza wrote:
> You must have a very fast machine! Any way, I get 5.647 and 43.134, respectively. The factor in both machines is close to 8, not 2 (what do you mean manually?)
> 
> -Tomas
> 
>> Date: Wed, 27 Oct 2010 05:13:59 -0400
>> From: sschmitt at physi.uni-heidelberg.de
>> Subject: [mg113391] Manually nested Tables faster than builtin nesting?
>> To: mathgroup at smc.vnet.net
>> 
>> Dear all!
>> 
>> I find that manually nested Tables are faster (factor 2 in my example)
>> compared to the builtin nesting. I probably do a stupid thinko. Could
>> you please have a look?
>> 
>> In[52]:= imax = jmax = 5000;
>> 
>> In[53]:= (tabletable = Table[Table[i*j, {i, imax}], {j, jmax}];) //
>>   Timing // First
>> 
>> Out[53]= 1.84
>> 
>> In[54]:= (table = Table[i*j, {i, imax}, {j, jmax}];) // Timing // First
>> 
>> Out[54]= 14.55
>> 
>> In[55]:= tabletable == table
>> 
>> Out[55]= True
>> 
>> Thanks,
>> 
>> Sebastian
>> 
>  		 	   		  



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