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MathGroup Archive 1993

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Speed When Accessing List Elements Sucks

  • To: mathgroup at yoda.physics.unc.edu
  • Subject: Speed When Accessing List Elements Sucks
  • From: "Michael S. Turok" <turok at cs.columbia.edu>
  • Date: Wed, 5 May 1993 02:47:51 -0400

Hi,

I have a list and I am trying to calculate the difference between
adjacent elements of the list:

	diff[[n]] = list[[n+1]] - list[[n]]

But it is taking forever!!  The list is about 100 elements long, and I
want to loop this about 50 times.  So, I am trying to create a diff 
matrix that is 50x100.  But, after 30 min. CPU time, only about 20
elements of the first row had been filled in!!!!

I tracked down the problem to the calculation of these differences,
and the real problem seems to be accessing of the elements themselves.
Can anyone please, please, please, help me, before I have to dump this
into C?

Thanks,
Michael





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