MathGroup Archive 2005

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Pattern Matching

  • To: mathgroup at
  • Subject: [mg58215] Pattern Matching
  • From: "Jeff" <jmcolon at>
  • Date: Thu, 23 Jun 2005 05:33:51 -0400 (EDT)
  • Sender: owner-wri-mathgroup at

Given a list of numbers, t = {0, -1, 0, -1, -2, -3, -4,-3,-4,-5}, I
would like to extract those numbers that are less than or equal to the
starting value by, for example, at least 2, but once the first (and
each subsequent) match is found, I would the starting value to drop by
2.  So for the list t, the output would be {-2, -4}.

I can use Cases or map using If[ ] on the list to extract those
elements that are less than or equal to -2, but I'm having difficutly
in figuring out how to change the starting value to be applied to
subsequent elements of the list.

Given my example, I could just extract all the multiples of 2 in the
list, but I would like the starting value to change by a fixed
percentage or combination of fixed number and percentage.


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