Bioequivalence and Bioavailability Forum • Floating point arithmetic, again

Floating point arithmetic, again [Software]

posted by Ohlbe – France, 2020-12-10 20:13 (281 d 02:21 ago) – Posting: # 22128
Views: 4,059

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:

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        To round or not to round… ElMaestro 2019-07-20 19:59
        
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- 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
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        Floating point arithmetic, again ElMaestro 2020-12-10 21:38
        
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