Bioequivalence and Bioavailability Forum • From bad to worse

From bad to worse [Software]

posted by mittyri – Russia, 2020-12-11 01:22 (1393 d 08:59 ago) – Posting: # 22136
Views: 10,860

Dear Ohlbe,

❝ If I get -2,77556E-17 when I type =(0.5-0.4-0.1), how comes that I get 0 when I type =(-0.1-0.4+0.5) ? The same figures, just in a different order ?

The order matters when you go to floating point arithmetic ;-)

❝ If I get FALSE when I type =0=0.5-0.4-0.1, how comes that I get TRUE when I type =0=-0.4-0.1+0.5 ?

Rightyright. Why did it happen? The root cause is described here
Excel does do some additional operations under the hood.

❝ And to be fair to Excel, the same happens in [image] :

❝

0==(0.5-0.4-0.1)

❝ [1] FALSE

❝ 0==(-0.4-0.1+0.5)

❝ [1] TRUE

❝ Are they first calculating -0.4-0.1=-0.5, which is nicely binarily coded, then -0.5+0.5=0 ?

Yes, take a look at this MS article
Both Excel and R are following IEEE 754, not surprising that the conditions are giving the same results. The problem is only in values representation to the user.

—
Kind regards,
Mittyri

Complete thread:

Spreadsheet failures, any recent examples? ElMaestro 2019-07-18 13:43 [Software]
- Spreadsheet failures, any recent examples? Ohlbe 2019-07-18 14:32
  - Spreadsheet addiction Helmut 2019-07-18 16:12
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    - Spreadsheet addiction Shuanghe 2019-07-18 18:59
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        OT: Spreadsheet addiction Helmut 2019-07-19 14:29
        
        OT: Spreadsheet addiction nobody 2019-07-19 15:53
        
        OT: Spreadsheet addiction Helmut 2019-07-19 19:32
  - Spreadsheet etc. failures zizou 2019-07-20 00:18
    - As designed ☺ Helmut 2019-07-20 02:12
      - As designed ☺ ElMaestro 2019-07-20 09:08
        
        To round or not to round… Helmut 2019-07-20 12:53
        
        To round or not to round… ElMaestro 2019-07-20 19:59
        
        floating-point math is always more complex than you think it is mittyri 2019-07-20 22:43
- Spreadsheet failures, any recent examples? Ohlbe 2020-12-10 18:43
  - Floating point arithmetic, again Helmut 2020-12-10 19:12
    - Floating point arithmetic, again ElMaestro 2020-12-10 19:40
      - Floating point arithmetic, again Ohlbe 2020-12-10 20:18
        
        Floating point arithmetic, again ElMaestro 2020-12-10 21:38
        
        Floating point arithmetic, again Ohlbe 2020-12-10 21:46
        
        Floating point arithmetic, again ElMaestro 2020-12-10 22:05
        
        Depressed Ohlbe 2020-12-10 23:35
        
        Depressed ElMaestro 2020-12-11 07:59
    - Floating point arithmetic, again Ohlbe 2020-12-10 20:13
  - From bad to worse Ohlbe 2020-12-10 22:11
    - From bad to worsemittyri 2020-12-11 00:22
    - All is good Helmut 2020-12-11 00:36
      - Float is float PharmCat 2020-12-18 20:53
        
        Float is float! Helmut 2020-12-20 23:27
        
        rational solution in R mittyri 2020-12-21 13:49
        
        related stuff Helmut 2021-01-14 12:53
        
        related stuff SDavis 2021-02-09 12:02
        
        related stuff ElMaestro 2021-02-09 19:55