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How to find computational complexity?

  1. Sep 4, 2007 #1
    If i have a program, how can i find the computational complexity? is there some other program i can run in the background?
     
  2. jcsd
  3. Sep 4, 2007 #2

    CRGreathouse

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    A first step would be counting the nested loops and looking at the number of times they execute. If you have three nested loops, each running from 1 to x, and inside the three you have operations taking constant time (i.e. not dependent on the size of any variable) then the complexity is [itex]\mathcal{O}(n^3)[/itex].

    If you're using bignums or the like you'll have to look into how much each operation costs based on the size of the numbers -- that's usually log(x)^k log(log(x))^n for some k and n. If you have a loop from 1 to x doing schoolbook multiplication on a bignum of size x, that's complexity [itex]\mathcal{O}(x(\log x)^2)[/itex].
     
    Last edited: Sep 4, 2007
  4. Sep 4, 2007 #3
    thanks for your help. can u point me to some resource where i can look some of this stuff up?
     
  5. Sep 5, 2007 #4

    dpm

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    If you're using standard library functions, most programming language standards will specify the mandatory asymptotic running time in the standard. If you're wanting to analyse your own code, then a good book (the standard in universities, pretty much), is Introduction to Algorithms by CLRS.
     
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