From: "Lawrence Velázquez" <vq@larryv.me>
To: Ray Andrews <rayandrews@eastlink.ca>
Cc: zsh-users@zsh.org
Subject: Re: run time of math problem
Date: Fri, 19 Mar 2021 19:46:16 -0400 [thread overview]
Message-ID: <A78ABFDE-07C4-40E5-A9CD-6DC3B2C45867@larryv.me> (raw)
In-Reply-To: <a1c6d13a-7a04-fba4-4419-7eccbf013824@eastlink.ca>
> On Mar 19, 2021, at 7:18 PM, Ray Andrews <rayandrews@eastlink.ca> wrote:
>
> ... 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.
Think about how your change affects your algorithm.
> 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: $divided
> done
Here, you evaluate "(level - 1.0) / level" 99 times.
> Now if I avoid the 'remainder' variable:
>
> for ((level=1; level<100; level++)); do
> sum=
> for ((terms=level; terms; terms--)); do
>
> # 'remainder' calculation done directly here:
> sum+=$(( ( (level - 1.0) / level )**(terms - 1) ))
> done
> divided=$(( sum * (1.0 / level) ))
> echo for level: $level, survival: $divided
> done
Here, you evaluate it 4950 times.
vq
next prev parent reply other threads:[~2021-03-19 23:47 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-19 23:18 Ray Andrews
2021-03-19 23:46 ` Lawrence Velázquez [this message]
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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