Re: Optimizing Memory Allocation in a Simple, but Long Function

From	Oscar Benjamin <oscar.j.benjamin@gmail.com>
Newsgroups	comp.lang.python
Subject	Re: Optimizing Memory Allocation in a Simple, but Long Function
Date	2016-04-26 10:54 +0100
Message-ID	<mailman.101.1461664511.32212.python-list@python.org> (permalink)
References	(10 earlier) <mailman.63.1461553965.32212.python-list@python.org> <do5vu5Fipb4U1@mid.individual.net> <CAHVvXxTU2k74S_hG=RtsEx=5uTk34Ppf4t2PhqBsat39Kv3ihQ@mail.gmail.com> <CAGuRns9w1bdScXdnhhD_COKftVaRm48y+RFMsCrBWF=mJcKnbw@mail.gmail.com> <CAHVvXxS5eTsrwGb65DpRxZ0bYDUVvt26Q5h2Arevm8zDRNKNaA@mail.gmail.com>

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On 25 April 2016 at 15:35, Derek Klinge <schilke.60@gmail.com> wrote:
>
> Although I see the value of relative error, I am just as interested in
> absolute error (though admittedly they are directly related values).

I was referring to relative error because the relative error is the
same at each step making the calculation of the global error easier.

> Are there modules or libraries I can/should use to minimize rounding error
> and use very large values of N and get an accurate answer?

from decimal import Decimal, localcontext

def e(prec):
    with localcontext() as ctx:
        ctx.prec = 2*prec + 1
        N = Decimal(10)**(prec)
        eapprox = (1 + 1/N)**N
        ctx.prec = prec
        return +eapprox

print(e(50))

Alternatively you can just use Decimal(1).exp().

> How does the math
> module calculate the vale of e?

https://hg.python.org/cpython/file/tip/Include/pymath.h#l54

--
Oscar

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Thread

Re: Optimizing Memory Allocation in a Simple, but Long Function Derek Klinge <schilke.60@gmail.com> - 2016-04-24 20:12 -0700
  Re: Optimizing Memory Allocation in a Simple, but Long Function Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2016-04-25 19:39 +1200
    Re: Optimizing Memory Allocation in a Simple, but Long Function Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2016-04-25 14:45 +0100
    Re: Optimizing Memory Allocation in a Simple, but Long Function Derek Klinge <schilke.60@gmail.com> - 2016-04-25 14:35 +0000
    Re: Optimizing Memory Allocation in a Simple, but Long Function Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2016-04-26 10:54 +0100

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