Bioequivalence and Bioavailability Forum

All is good [Software]

posted by Helmut  – Vienna, Austria, 2020-12-11 01:36 (1462 d 13:01 ago) – Posting: # 22137
Views: 17,319

Hi Ohlbe,

❝ … the same happens in :

So you installed this goody at last?

❝

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?

Would have to dive into the lexer of the source of base-. Likely not clever enough anyway. If you want to explore the matter, type ?Syntax, ?Arithmetic, ?Comparison, and their relatives. See also the (in)famous FAQ 7.31. However, the `==` operator should not be used to compare two objects for identity. Otherwise we fall into the binary trap:

x1 <- (0.5-0.4-0.1)
x2 <- (-0.4-0.1+0.5)
x1; x2
[1] -2.775558e-17
[1] 0
x1 == x2
[1] FALSE
identical(x1, x2)
[1] FALSE
all.equal(x1, x2)
[1] TRUE

Only the last function compares to the numeric precision of the machine* and this is what we want and the best we can hope for…

---

• On my machine with 64bit  …
  sqrt(.Machine$double.eps)
[1] 1.490116e-08
  … which is orders of magnitude larger than abs(-2.775558e-17) – which is just “noise”. Hence, the test passes.
  x1 <- (0.5-0.4-0.1)
x2 <- (-0.4-0.1+0.5)
sqrt(.Machine$double.eps) > abs(x1 - x2)
[1] TRUE
  That’s a crude example. The source is more tricky. Try getAnywhere(all.equal.numeric) to see the 77 lines of source code fo comparing numbers.

—
Dif-tor heh smusma 🖖🏼 Довге життя Україна! 
Helmut Schütz


The quality of responses received is directly proportional to the quality of the question asked. 🚮
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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, again Ohlbe 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 goodHelmut 2020-12-11 00:36
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          • Float is float! Helmut 2020-12-20 23:27
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                  • related stuff ElMaestro 2021-02-09 19:55