Bioequivalence and Bioavailability Forum • Floating point arithmetic, again

Floating point arithmetic, again [Software]

posted by Ohlbe – France, 2020-12-10 20:13 (561 d 14:53 ago) – Posting: # 22128
Views: 6,174

Dear Helmut,

» OK, write in A1 =0.5-0.4-0.1 and in B1 =A1=0

» 1. What do you expect?

I expect A1 to read 0. Regarding B1: I would naturally expect it to return TRUE. But on the other hand, typing =0=0.5-0.4-0.1 returns FALSE, and I would not necessarily expect a two-step calculation to yield a result that differs from a one-step calculation. By the way I checked: =0=5-4-1 returns TRUE, so it is not that Excel just compares 0 to 0.5 and ignores the subsequent signs and figures.

» 2. What do you get?

A1 returns 0, as expected. Switching to scientific notation gives 0,00E+00. So it doesn't look like we have some hidden decimals there that don't show because of the default display.

B1 returns TRUE. Indeed the result I would normally expect. But this means that typing the comparison and the calculation in one cell, or the calculation in one cell and the comparison in another, gives different results.

» Try in A1 =16-8-4-2-2, in B1 =(16-8-4-2-2), and in C1 =A1=B1. I bet it “works” as expected, since these numbers can be converted to binary digits without error.

Yes. But it works also with A1 =5-4-1, in B1 =(5-4-1), and in C1 =A1=B1. So it works with 5, which is not a power of 2 ?

—
Regards
Ohlbe

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
    - Nasty beast Ohlbe 2019-07-18 17:30
      - Nasty beast Helmut 2019-07-18 20:26
        
        Nasty beast Ohlbe 2019-07-19 11:32
        
        Nasty beast ElMaestro 2019-07-19 12:32
        
        Decidedly off topic Ohlbe 2019-07-19 13:38
        
        OT: R limbo 101 Helmut 2019-07-19 13:00
    - Spreadsheet addiction Shuanghe 2019-07-18 18:59
      - Spreadsheet addiction Helmut 2019-07-18 20:04
        
        OT: Spreadsheet addiction Shuanghe 2019-07-19 12:41
        
        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, againOhlbe 2020-12-10 20:13
  - From bad to worse Ohlbe 2020-12-10 22:11
    - From bad to worse mittyri 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