Re^2: Small Perl 6 discoveries II, Rats

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Re^3: Small Perl 6 discoveries II, Rats by syphilis (Archbishop) on Oct 20, 2017 at 04:12 UTC
If you want arbitrary precision rational arithmetic, you can use a FatRat I didn't know about FatRats (yes, I know very little about perl6) - so I had a bit of a play (on rakudo-star-2017.07) and encountered confusing results: `> my $x = 1.111111111111111111111.FatRat; my $y = 1.111111111111111111 +111.Rat; $x - $y 0 > $x == $y True > say $x 1.111111111111111111111 > say $y 1.11111111111111111604544 >` [download] On the bases that `$x-$y==0` and `$x==$y` one is led to believe that $x and $y are exactly equivalent. Yet, say() presents us with different values. Are the 2 rationals equivalent ? If so, then why does say() output different values ? If not, then why do both `$x-$y==0` and `$x==$y` evaluate as "True" ? Interestingly, 1.11111111111111111604544 is the value of the double 1.1111111111111111 (16 decimal places) rounded to 23 decimals: `C:\>perl -le "printf '%.22e\n', 1.1111111111111111;" 1.1111111111111111604544e+000\n` [download] Perhaps this ties in with: `> my $x = 1.111111111111111111111.FatRat; my $y = 1.1111111111111111.N +um; $x - $y 0 > $x == $y True` [download] How does one coerce perl6 into displaying the actual numerator and denominator of these rationals ? Cheers, Rob	[reply] [d/l] [select]
Re^4: Small Perl 6 discoveries II, Rats by Anonymous Monk on Oct 20, 2017 at 15:02 UTC
How does one coerce perl6 into displaying the actual numerator and denominator of these rationals? `$x.nude` That would make sense if the numerator and denominator were `$x.nu` and `$x.de`, but they're not. You have to type out `$x.numerator` and `$x.denominator`. I thought we were trying to make Perl6 safe for 10-year-old girls, but I guess someone just couldn't pass up an opportunity for a crude joke.	[reply]
Re^5: Small Perl 6 discoveries II, Rats by syphilis (Archbishop) on Oct 22, 2017 at 11:34 UTC
`$x.nude` That enables me to see that 1.111111111111111111111.FatRat and 1.111111111111111111111.Rat have equivalent rational values: `> my $x = 1.111111111111111111111.Rat; $x.nude (1111111111111111111111 1000000000000000000000) > my $y = 1.111111111111111111111.FatRat; $y.nude (1111111111111111111111 1000000000000000000000)` [download] and that $x (the Rat) gets handled in a way that I don't really expect: `> my $r1 = $x * 0.3 0.333333333333333 > $r1 = $x * 0.3.Rat 0.333333333333333 > $r1 = $x * 0.3.Num 0.333333333333333 > $r1 = $x * 3e-1 0.333333333333333 > $r1 = $x * 0.3.FatRat 0.3333333333333333333333` [download] though the last result is as I expected. Compare those outputs with: `> my $r2 = $y * 0.3 0.3333333333333333333333 > my $r2 = $y * 0.3.Rat 0.3333333333333333333333 > my $r2 = $y * 0.3.Num 0.333333333333333 > my $r2 = $y * 3e-1 0.333333333333333 > my $r2 = $y * 0.3.FatRat 0.3333333333333333333333` [download] which is more in keeping with my expectations. I'm sure it all makes sense if you know how to look at it from the appropriate angle. Cheers, Rob	[reply] [d/l] [select]
Re^6: Small Perl 6 discoveries II, Rats by Anonymous Monk on Oct 22, 2017 at 15:14 UTC
Re^7: Small Perl 6 discoveries II, Rats by syphilis (Archbishop) on Oct 22, 2017 at 23:12 UTC
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Re^3: Small Perl 6 discoveries II, Rats by Anonymous Monk on Oct 19, 2017 at 15:52 UTC
If the `Rat` class isn't any more accurate than a `Num`, but it's much slower, then what purpose does it serve?	[reply]
Re^4: Small Perl 6 discoveries II, Rats by bduggan (Pilgrim) on Oct 19, 2017 at 16:02 UTC
Well -- I'd say it is more accurate (though not more precise) -- it can accurately represent rational numbers, so you can do rational arithmetic without rounding errors. e.g. `> .3.Num - .2.Num - .1.Num == 0 False > .3 - .2 - .1 == 0 True` [download]	[reply] [d/l]
Re^5: Small Perl 6 discoveries II, Rats by Anonymous Monk on Oct 19, 2017 at 16:44 UTC
The reason this digression started is because it can't accurately represent rational numbers. Except for trivial examples, I suppose.	[reply]


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