Re: How about adding rational fraction to Python?

On Feb 16, 6:50�pm, Carl Banks <pavlovevide...@xxxxxxxxx> wrote:
On Feb 16, 5:51 pm, Jeff Schwab <j...@xxxxxxxxxxxxxxxx> wrote:

Carl Banks wrote:
On Feb 16, 3:03 pm, Lie <Lie.1...@xxxxxxxxx> wrote:
Although rationals have its limitations too, it is a much
better choice compared to floats/Decimals for most cases.

Maybe that's true for your use cases, but it's not true for most cases
in general.

Rationals are pretty useless for almost any extended calculations,
since the denominator tends to grow in size till it's practically
unusbale,

What do you mean by "practically unusable?"

So big that a fraction takes 10 minutes to reduce to simplest form and/
or your hard disk starts thrashing.

Out of curiosity, just how big is that?
I ask because I routinely use extremely big
ints and rationals and haven't seen that.

And I'm talking about numbers with, say,
50000 decimal digits up to numbers with
over a billion bits.


It can easily happen with seemingly innocuous calculations.

Where I've had problems is not the size
of the numbers in the repeated calculations
but the number of calculations, say, millions.


I heard similar arguments
made against big integers at one point ("Primitive types are usually big
enough, why risk performance?") but I fell in love with them when I
first saw them in Smalltalk, and I'm glad Python supports them natively.

It's not the same argument, though.

Repeated calculations don't make bignums too large to manage unless
they're growing it exponentially.

My work grows exponentially.


With rationals, the accumulating calculations usually makes the
denominator grow out of control (unless there's some mitigating
factor, like in Paul Rubin's example where there were only a ever few
denominators.)

I don't see any problem there either.

It's entirely possible _I_ won't be able
to use the new Fraction data type. My work
has already left the built-in Python big
ints in the dust in favor of gmpy, so I
have no expectation that the new Fraction
type will be of any use to me.


Carl Banks

.

Relevant Pages

  • naive questions about nested intervals with Farey fractions
    ... in a table as the numerator and denominator of a rational number, ... possible to calculate the rational numbers to double precision, ... the values up and store them in single precision cells, then execute ... requires no calculations beyond the booleans within the SELECT ...
    (comp.databases.theory)
  • Re: limits help
    ... using taylor expansion, to expanding the denominator in the fraction ... wikipedia on the series expansion of y = coth x and multiplying it by ...
    (sci.math)
  • Re: Fractions
    ... But 1/8 *is* part of the font. ... Word MVP FAQ site: http://word.mvps.org ... > formatting fraction existing in your document, ... > Dim Expr, Numerator, Denominator, NewSlashChar As String ...
    (microsoft.public.word.newusers)
  • Re: Fractions
    ... character for 1/8 is not". ... Greg Maxey ... >> formatting fraction existing in your document, ... >> Dim Expr, Numerator, Denominator, NewSlashChar As String ...
    (microsoft.public.word.newusers)
  • Re: limits help
    ... using taylor expansion, to expanding the denominator in the fraction ... wikipedia on the series expansion of y = coth x and multiplying it by ...
    (sci.math)