From: tadayoshi funaba <redmine@...>
Date: 2009-06-18T07:43:41+09:00
Subject: [ruby-core:23906] [Bug #1640] [PATCH] Documentation for the Rational Class

Issue #1640 has been updated by tadayoshi funaba.


>> div and modulo relate to floor, remainder relate to truncate.
>
> Do you suggest a "see also" pointer between these methods, or did you want something else?

i think many programmer don't understand differences between modulo
and remainder.

"If _rat_ and _numeric_ have different signs, returns _mod_-_numeric_..."
it's so difficult for me.

x modulo y = x-y*floor(x/y)
x remainder y = x-y*truncate(x/y)

x = Rational(13); y = Rational(-4)
x-y*(x/y).floor #=> (-3/1)
x-y*(x/y).truncate #=> (1/1)

x.modulo(y) #=> (-3/1)
x.remainder(y) #=> (1/1)

and

x-y*(x/y).div(1)#=> (-3/1) # modulo

>> floor, ceil and truncate can accept an extra argument, not only round.
>
>Yes, I realised that. I didn't document them because I was waiting for an explanation of how that argument worked. Could you explain it to me? :-)

same.
floor (-inf), ceil (+inf), truncate (zero) and round (nearest)

'%f' % Rational('-1.125').floor(2) #=> "-1.130000"
'%f' % Rational('-1.125').ceil(2) #=> "-1.120000"
'%f' % Rational('-1.125').truncate(2) #=> "-1.120000"
'%f' % Rational('-1.125').round(2) #=> "-1.130000"

'%f'% ((Rational('-1.125')*10**2).floor*10**-2) #=> "-1.130000"
'%f'% ((Rational('-1.125')*10**2).ceil*10**-2) #=> "-1.120000"
'%f'% ((Rational('-1.125')*10**2).truncate*10**-2) #=> "-1.120000"
'%f'% ((Rational('-1.125')*10**2).round*10**-2) #=> "-1.130000"

also accept negative number.

'%f' % Rational('12345.6789').round(2) #=> "12345.680000"
'%f' % Rational('12345.6789').round(-2) #=> "12300.000000"

see also Float#round.

12345.6789.round(2) #=> 12345.68
12345.6789.round(-2) #=> 12300

>> to_r also, but never raise exception of parser error.
>
>I don't understand this. Rational() doesn't call #to_r on arguments, and does raise errors for invalid arguments. Could you clarify?

it's ruby's style.

$ ruby -e 'p Integer("x")'
-e:1:in `Integer': invalid value for Integer: "x" (ArgumentError)
	from -e:1

$ ruby -e 'p Integer(nil)'
-e:1:in `Integer': can't convert nil into Integer (TypeError)
	from -e:1:in `<main>'

$ ruby -e 'p Integer(Integer(Integer("0")))'
0

$ ruby -e 'p "x".to_i'
0

Thanks for your re-edit.

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