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From: Bradley Hintze on 12 Aug 2010 16:43
Hi all.

Is there a way I can keep my floating point number as I typed it? For
example, I want 34.52 to be 34.52 and NOT 34.5200000002.

--
Bradley J. Hintze
Graduate Student
Duke University
School of Medicine
801-712-8799
From: Grant Edwards on 12 Aug 2010 17:20
On 2010-08-12, Bradley Hintze <bradley.h(a)aggiemail.usu.edu> wrote:

> Is there a way I can keep my floating point number as I typed it?

No.

> For example, I want 34.52 to be 34.52 and NOT 34.5200000002.

You can't represent 34.52 using base-2 IEEE floating point (the HW
floating point format used by pretty much all modern computers).
34.5200000002 is as close as you can get.

When you enter a base-10 floating-point number, the computer will use
the closest base-2 IEEE floating point number.

Here are the nitty-gritty details:

http://docs.sun.com/source/806-3568/ncg_goldberg.html

Can you explain what your actual problem is?

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Grant Edwards grant.b.edwards Yow! I'm imagining a surfer
at van filled with soy sauce!
gmail.com
From: Grant Edwards on 12 Aug 2010 17:24
On 2010-08-12, Grant Edwards <invalid(a)invalid.invalid> wrote:
> On 2010-08-12, Bradley Hintze <bradley.h(a)aggiemail.usu.edu> wrote:
>
>> Is there a way I can keep my floating point number as I typed it?
>
> No.
>
>> For example, I want 34.52 to be 34.52 and NOT 34.5200000002.
>
> You can't represent 34.52 using base-2 IEEE floating point (the HW
> floating point format used by pretty much all modern computers).
> 34.5200000002 is as close as you can get.
>
> When you enter a base-10 floating-point number, the computer will use
> the closest base-2 IEEE floating point number.
>
> Here are the nitty-gritty details:
>
> http://docs.sun.com/source/806-3568/ncg_goldberg.html

Here is a gentler intro:

http://pyfaq.infogami.com/why-are-floating-point-calculations-so-inaccurate

--
Grant Edwards grant.b.edwards Yow! If I felt any more
at SOPHISTICATED I would DIE
gmail.com of EMBARRASSMENT!
From: Grant Edwards on 12 Aug 2010 17:25
On 2010-08-12, Grant Edwards <invalid(a)invalid.invalid> wrote:

>> Here are the nitty-gritty details:
>>
>> http://docs.sun.com/source/806-3568/ncg_goldberg.html
>
> Here is a gentler intro:
>
> http://pyfaq.infogami.com/why-are-floating-point-calculations-so-inaccurate

And another good page:

http://docs.python.org/tutorial/floatingpoint.html

--
Grant Edwards grant.b.edwards Yow! I feel like I'm
at in a Toilet Bowl with a
gmail.com thumbtack in my forehead!!
From: Philip Semanchuk on 12 Aug 2010 17:25

On Aug 12, 2010, at 4:43 PM, Bradley Hintze wrote:

> Hi all.
>
> Is there a way I can keep my floating point number as I typed it? For
> example, I want 34.52 to be 34.52 and NOT 34.5200000002.

Hi Bradley,
Use the Decimal type instead. It's not as convenient as float, but it
will give you a consistent representation of your numbers.

The behavior of floating point numbers surprises a lot of people and
has been discussed at length a number of times here (and elsewhere).

If you're in the mood for EXTREMELY thorough coverage of the subject,
you can read this:
http://docs.sun.com/source/806-3568/ncg_goldberg.html

There's a gentler discussion of it here:
http://en.wikipedia.org/wiki/Floating_point#Representable_numbers.2C_conversion_and_rounding

HTH
Philip
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