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From: Ray Andrews <rayandrews@eastlink.ca>
To: Zsh Users <zsh-users@zsh.org>
Subject: run time of math problem
Date: Fri, 19 Mar 2021 16:18:13 -0700	[thread overview]
Message-ID: <a1c6d13a-7a04-fba4-4419-7eccbf013824@eastlink.ca> (raw)

This question might not even be answerable and it's only a point of 
interest:
I was working out some probabilities and the algorithm looks like this:

    for ((level=1; level<100; level++)); do
         sum=
         remainder=$(( (level - 1.0) / level ))
         for ((terms=level; terms; terms--)); do
             sum+=$(( remainder**(terms - 1) ))
         done
         divided=$(( sum * (1.0 / level) ))
         echo for level: $level, survival: $divided
    done

Now if I avoid the 'remainder' variable:

     for ((level=1; level<100; level++)); do
         sum=
         for ((terms=level; terms; terms--)); do

             # 'remainder' calculation done directly here:
             sum+=$(( ( (level - 1.0) / level )**(terms - 1) ))
         done
         divided=$(( sum * (1.0 / level) ))
         echo for level: $level, survival: $divided
    done

... I'd expect the thing to run a teeny bit faster but in fact it
runs about 15% slower.  Is that explicable?  Does zsh prefer
calculations done in steps with variables for each step?  Or is this
just some little anomaly?  Things might not optimize every time.





             reply	other threads:[~2021-03-19 23:18 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-19 23:18 Ray Andrews [this message]
2021-03-19 23:46 ` Lawrence Velázquez
2021-03-19 23:51   ` Ray Andrews
2021-03-19 23:52 ` Oliver Kiddle
2021-03-20  2:40   ` Ray Andrews
2021-03-20  3:59     ` Lawrence Velázquez

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