R devel - Aug 2009 - Accuracy (PR#13867)

Full_Name: Manuel Luethi
Version: 2.9.1
OS: Windows XP
Submission from: (NULL) (129.132.128.136)


Hi

I created the following vectors:

p_1=c(0.2,0.2,0.2,0.2,0.1,0.25,0.4,0.1,0.25,0.4,0.1,0.25,0.4,0.1,0.25,0.4,0.2,0.5,0.8,0.2,0.5,0.8,0.2,0.5,0.8,0.2,0.5,0.8)
p_2=c(0,0,0,0,0.5,0.5,0.5,0.5,0.5,0.5,0.5,0.5,0.5,0.5,0.5,0.5,0.4,0.25,0.1,0.4,0.25,0.1,0.4,0.25,0.1,0.4,0.25,0.1)

As these are probabilities, I calculated the remainder as

p_3=1-p_1-p_2

There the values which ought to be 0.1 were lateron not recognised by p_3==0.1,
but only if I used p_3 <= 0.1.

The full calculation is actually bigger but the core issue remains: I used
values input by hand, built a difference and it was wrong.

I know that exactly the value 0.1 is one that can not be represented using
binary rep. Maybe that's it, maybe not. Just wanted to let you know.

With kind regards

Manuel

On Tue, Aug 04, 2009 at 04:25:09PM +0200, luethman at student.ethz.ch
wrote:
> Hi
> 
> I created the following vectors:
> 
>
p_1=c(0.2,0.2,0.2,0.2,0.1,0.25,0.4,0.1,0.25,0.4,0.1,0.25,0.4,0.1,0.25,0.4,0.2,0.5,0.8,0.2,0.5,0.8,0.2,0.5,0.8,0.2,0.5,0.8)
>
p_2=c(0,0,0,0,0.5,0.5,0.5,0.5,0.5,0.5,0.5,0.5,0.5,0.5,0.5,0.5,0.4,0.25,0.1,0.4,0.25,0.1,0.4,0.25,0.1,0.4,0.25,0.1)
> 
> As these are probabilities, I calculated the remainder as
> 
> p_3=1-p_1-p_2
> 
> There the values which ought to be 0.1 were lateron not recognised by
p_3==0.1,
> but only if I used p_3 <= 0.1.
> 
> The full calculation is actually bigger but the core issue remains: I used
> values input by hand, built a difference and it was wrong.
> 
> I know that exactly the value 0.1 is one that can not be represented using
> binary rep. Maybe that's it, maybe not.
Yes, this is the problem. In this case, one can obtain a correct
result using round()

  p1 <- c(0.2,0.2,0.2,0.2,0.1,0.25,0.4,0.1,0.25,0.4,0.1,0.25,0.4,0.1,
          0.25,0.4,0.2,0.5,0.8,0.2,0.5,0.8,0.2,0.5,0.8,0.2,0.5,0.8)
  p2 <- c(0,0,0,0,0.5,0.5,0.5,0.5,0.5,0.5,0.5,0.5,0.5,0.5,0.5,0.5,0.4,
          0.25,0.1,0.4,0.25,0.1,0.4,0.25,0.1,0.4,0.25,0.1)
  p3 <- 1 - p1 - p2
  round(p3, 2) == 0.1
  #  [1] FALSE FALSE FALSE FALSE FALSE FALSE  TRUE FALSE FALSE  TRUE FALSE FALSE
  # [13]  TRUE FALSE FALSE  TRUE FALSE FALSE  TRUE FALSE FALSE  TRUE FALSE FALSE
  # [25]  TRUE FALSE FALSE  TRUE

Petr.

What research into this problem did you do that failed to turn up FAQ 7.31?

-- 
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow at imail.org
801.408.8111

> -----Original Message-----
> From: r-devel-bounces at r-project.org [mailto:r-devel-bounces at r-
> project.org] On Behalf Of luethman at student.ethz.ch
> Sent: Tuesday, August 04, 2009 8:25 AM
> To: r-devel at stat.math.ethz.ch
> Cc: R-bugs at r-project.org
> Subject: [Rd] Accuracy (PR#13867)
> 
> Full_Name: Manuel Luethi
> Version: 2.9.1
> OS: Windows XP
> Submission from: (NULL) (129.132.128.136)
> 
> 
> Hi
> 
> I created the following vectors:
> 
> p_1=c(0.2,0.2,0.2,0.2,0.1,0.25,0.4,0.1,0.25,0.4,0.1,0.25,0.4,0.1,0.25,0
> .4,0.2,0.5,0.8,0.2,0.5,0.8,0.2,0.5,0.8,0.2,0.5,0.8)
> p_2=c(0,0,0,0,0.5,0.5,0.5,0.5,0.5,0.5,0.5,0.5,0.5,0.5,0.5,0.5,0.4,0.25,
> 0.1,0.4,0.25,0.1,0.4,0.25,0.1,0.4,0.25,0.1)
> 
> As these are probabilities, I calculated the remainder as
> 
> p_3=1-p_1-p_2
> 
> There the values which ought to be 0.1 were lateron not recognised by
> p_3==0.1,
> but only if I used p_3 <= 0.1.
> 
> The full calculation is actually bigger but the core issue remains: I
> used
> values input by hand, built a difference and it was wrong.
> 
> I know that exactly the value 0.1 is one that can not be represented
> using
> binary rep. Maybe that's it, maybe not. Just wanted to let you know.
> 
> With kind regards
> 
> Manuel
> 
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel

What research into this problem did you do that failed to turn up FAQ 7.31?

--=20
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow at imail.org
801.408.8111

> -----Original Message-----
> From: r-devel-bounces at r-project.org [mailto:r-devel-bounces at r-
> project.org] On Behalf Of luethman at student.ethz.ch
> Sent: Tuesday, August 04, 2009 8:25 AM
> To: r-devel at stat.math.ethz.ch
> Cc: R-bugs at r-project.org
> Subject: [Rd] Accuracy (PR#13867)
>=20
> Full_Name: Manuel Luethi
> Version: 2.9.1
> OS: Windows XP
> Submission from: (NULL) (129.132.128.136)
>=20
>=20
> Hi
>=20
> I created the following vectors:
>=20
> p_1=3Dc(0.2,0.2,0.2,0.2,0.1,0.25,0.4,0.1,0.25,0.4,0.1,0.25,0.4,0.1,0.25,0
> .4,0.2,0.5,0.8,0.2,0.5,0.8,0.2,0.5,0.8,0.2,0.5,0.8)
> p_2=3Dc(0,0,0,0,0.5,0.5,0.5,0.5,0.5,0.5,0.5,0.5,0.5,0.5,0.5,0.5,0.4,0.25,
> 0.1,0.4,0.25,0.1,0.4,0.25,0.1,0.4,0.25,0.1)
>=20
> As these are probabilities, I calculated the remainder as
>=20
> p_3=3D1-p_1-p_2
>=20
> There the values which ought to be 0.1 were lateron not recognised by
> p_3=3D=3D0.1,
> but only if I used p_3 <=3D 0.1.
>=20
> The full calculation is actually bigger but the core issue remains: I
> used
> values input by hand, built a difference and it was wrong.
>=20
> I know that exactly the value 0.1 is one that can not be represented
> using
> binary rep. Maybe that's it, maybe not. Just wanted to let you know.
>=20
> With kind regards
>=20
> Manuel
>=20
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel