irb(main):084:0> (-1.0/0.0)

=> -Infinity

irb(main):086:0> (1.0/0.0)

=> Infinity

but

irb(main):087:0> Infinity

NameError: uninitialized constant Infinity

from (irb):87

from :0

is it possible to directly access/create a float representing positive

or negative infinity?

Thanks,

Hadley

On Sun, Jul 23, 2006 at 04:22:37AM +0900, hadley wickham wrote:

```
from :0
```

is it possible to directly access/create a float representing positive

or negative infinity?

Infinity = 1.0/0

(N.B. Doesn’t work on all platforms.)

marcel

Infinity = 1.0/0

(N.B. Doesn’t work on all platforms.)

But it will everywhere that supports the IEEE floating point standard?

Thanks,

Hadley

Others have answered the main question here but it’s worth noting for

the future that just because it says infinity doesn’t mean a constant

exists with that name. Check this out:

irb(main):001:0> class A; end

=> nil

irb(main):002:0> class B; end

=> nil

irb(main):003:0> A, B = B, A

(irb):3: warning: already initialized constant A

(irb):3: warning: already initialized constant B

=> [B, A]

irb(main):004:0> A

=> B

irb(main):005:0> B

=> A

The name is independent of constants.

On 7/22/06, hadley wickham [email protected] wrote:

```
from (irb):87
from :0
```

is it possible to directly access/create a float representing positive

or negative infinity?

Thanks,

Hadley

#!/usr/bin/ruby

InfinityClass = Class.new

Infinity = InfinityClass.new

class << InfinityClass

def new; Infinity end

end

class InfinityClass

def method_missing(name, *args, &blk )

Infinity

end

def to_s; “biiig”; end

end

puts Infinity

puts Infinity + 1

puts 3 * Infinity

unfortunately in order to make the last work you have to redefine

Fixnum#*

etc etc which does not

seem pratical and I suppose that Infinity should be returned under

certain

circumstances which means that

in an expression like

a op b, b could easily be Infinity

Cheers

Robert

Infinity = " a heck of a long time"

#
Sorry could not resist

##
I suppose you would like things like

Infinity * 3 = Infinity etc. etc.

Deux choses sont infinies : l’univers et la bÃªtise humaine ; en ce qui

concerne l’univers, je n’en ai pas acquis la certitude absolue.

On 7/22/06, Marcel Molina Jr. [email protected] wrote:

Infinity = 1.0/0

(N.B. Doesn’t work on all platforms.)

Does anyone know a definition for Infinity that does work on all

platforms? Here’s what I use; I have no idea how robust it really is:

Infinity= begin

result= [ Float::MAX**Float::MAX, Float::MAX**2, Float::MAX*2].max

result.infinite? ? result : result=1.0/0

rescue: Float::MAX #maybe 1.0/0 doesn’t work on some systems?

end unless defined? Infinity

#there’s also this way:

999999999999999999999999999999999999999999999999e99999999999999999

#but stuff like that sometimes returns zero, so it doesn’t seem as

reliable.

#(plus it generates a warning)

Others have answered the main question here but it’s worth noting for

the future that just because it says infinity doesn’t mean a constant

exists with that name. Check this out:

Yes, but a lot of languages provide some way of accessing the

“constants” that represent special floating point numbers: Inf, -Inf

and NaN

Hadley

Facets has Infinity (actaully it was deprecated for a while until I

fixed. Your post inspired me to fix it, so it’s now back in the very

latest version. Thanks!)

It uses the constant INFINITY. Is that cool? Or is there some sort of

general practice of using Inf?

Thanks,

T.

Yes, but a lot of languages provide some way of accessing the

“constants” that represent special floating point numbers: Inf, -Inf

and NaN

I think Matz vetoed anything that required IEEE floating point a little

while ago. So … for Ruby code to use Inf, -Inf or NaN, there would

need to be special care taken to maintain portability.

Thanks for that explanation, although it does worry me a little, I

understand that getting floating point working precisely correctly

across multiple platforms is very hard.

Regards,

Hadley

Facets has Infinity (actaully it was deprecated for a while until I

fixed. Your post inspired me to fix it, so it’s now back in the very

latest version. Thanks!)

That’s great! Thanks.

It uses the constant INFINITY. Is that cool? Or is there some sort of

general practice of using Inf?

I think Inf is more common: R uses it, so does MATLAB

(Create array of all Inf values - MATLAB Inf),

and there’s a PEP for python that uses it

(PEP 754 – IEEE 754 Floating Point Special Values | peps.python.org, which also has a nice

discussion of these issues)

Hadley

hadley wickham wrote:

(Create array of all Inf values - MATLAB Inf),

and there’s a PEP for python that uses it

(PEP 754 – IEEE 754 Floating Point Special Values | peps.python.org, which also has a nice

discussion of these issues)

Nice, that was helpful. I added some query methods to Numeric, eg.

finite?, infinite?, … and did this:

UNDEFINED = InfinityClass.instance(0)

INFINITY = InfinityClass.instance(1)

NaN = UNDEFINED

Inf = INFINITY

PosInf = INFINITY

NegInf = -INFINITY

Thanks!

T.

Nice, that was helpful. I added some query methods to Numeric, eg.

finite?, infinite?, … and did this:

UNDEFINED = InfinityClass.instance(0)

INFINITY = InfinityClass.instance(1)

NaN = UNDEFINED

Inf = INFINITY

PosInf = INFINITY

NegInf = -INFINITY

Great. Note that (NaN == NaN) == False, but I think the rest of the

relations are straightforward.

Hadley

In article [email protected],

“M. Edward (Ed) Borasky” [email protected] writes:

Some important vendors of such equipment – Cray, FPS and IBM – adhered

to neither of these standards. Digital/Compaq/HP adopted it for the

Alphas but kept the Vax line at its historic format for compatibility.

But *new* architectures almost entirely adopted IEEE – there is little

reason not to do so. At some point in the evolution of Ruby, the number

of actual users of non-IEEE platforms will be negligible. Just out of

curiosity, how many users of non-IEEE Ruby are there on this list, and

what fraction of the total list membership does that represent? Feel

free to decline to answer if you’re in a classified shop.

Some time ago, I installed Ruby on NetBSD/vax on SIMH.

http://www.netbsd.org/Ports/vax/

http://simh.trailing-edge.com/

It is fine until make.

But make test fails because 0.0/0 fails.

I guess VAX has no NaN.

I think no one try to fix it.

Note that I also installed Ruby on Debian for S/390 on Hercules.

http://www.debian.org/ports/s390/

http://www.conmicro.cx/hercules/

Unexpectedly, Ruby works fine on S/390.

After some investigation, I found that newer models have

IEEE registers and Linux kernel emulates them for old

models.

http://www.linuxbase.org/spec/ELF/zSeries/lzsabi0_s390.html

hadley wickham wrote:

Yes, but a lot of languages provide some way of accessing the

“constants” that represent special floating point numbers: Inf, -Inf

and NaN

I think Matz vetoed anything that required IEEE floating point a little

while ago. So … for Ruby code to use Inf, -Inf or NaN, there would

need to be special care taken to maintain portability.

Thanks for that explanation, although it does worry me a little, I

understand that getting floating point working precisely correctly

across multiple platforms is very hard.

Which is *precisely* why dozens of hard core applied mathematicians and

computer scientists, the IEEE and SIAM (Society for Industrial and

Applied Mathematics), and nearly every vendor of equipment intended for

scientific computing, both large and small, developed and embraced the

IEEE standards! Note that there are actually *two* IEEE standards. The

one most of us think of is the 32-bit/64-bit one that’s implemented in

Intel hardware. However, there was another looser standard which did not

specify bit for bit behavior but only the computational requirements.

The IEEE floating point standards are happy exceptions to the rule that

nothing good was ever designed by a committee.

Some important vendors of such equipment – Cray, FPS and IBM – adhered

to neither of these standards. Digital/Compaq/HP adopted it for the

Alphas but kept the Vax line at its historic format for compatibility.

But *new* architectures almost entirely adopted IEEE – there is little

reason not to do so. At some point in the evolution of Ruby, the number

of actual users of non-IEEE platforms will be negligible. Just out of

curiosity, how many users of non-IEEE Ruby are there on this list, and

what fraction of the total list membership does that represent? Feel

free to decline to answer if you’re in a classified shop.