- Pharo-users - lists.pharo.org

Re: Rounding in Floats

by Steffen MÃ¤rcker

Have you considered using fixed-point arithmetic? For example: 7.1s2 roundTo: 0.1s2 The rule of thumb I stick to is to use FP only if I know the inaccuracies won't bite me. Funny enough, both 7.1 and 0.1 are already not accurately representable as floats. (And by coincidence, I prepared exam questions about floats for my students yesterday. ) Kind regards, Steffen Konrad Hinsen schrieb am Dienstag, 15. Juni 2021 07:02:30 (+02:00): > On 15/06/2021 01:03, Esteban Maringolo wrote: > > Sure, but what initiated this thread was a reference to roundTo: 0.1 > > which produced a "wrong" output. > > > > (9.1 + (-2.0)) roundTo: 0.1 "=> 7.1000000000000005" > > 7.1 roundTo: 0.1 "=> 7.1000000000000005" > > > > However, at this point I know that Pharo "does the right, raw, thing" > > (at least compared to other mainstream languages), but it still > > produces a surprise effect. > > That's the "floating point surprise" that everyone has at some point, no matter the language and runtime system. If that surprise is a problem for you, are you sure that floating-point arithmetic is what you really want? Maybe your needs are better served with integers and fractions. > > > Konrad. > > -- Gesendet mit Vivaldi Mail. Laden Sie Vivaldi kostenlos von vivaldi.com herunter.

June 15, 2021

Re: Rounding in Floats

by Konrad Hinsen

On 15/06/2021 01:03, Esteban Maringolo wrote: > Sure, but what initiated this thread was a reference to roundTo: 0.1 > which produced a "wrong" output. > > (9.1 + (-2.0)) roundTo: 0.1 "=> 7.1000000000000005" > 7.1 roundTo: 0.1 "=> 7.1000000000000005" > > However, at this point I know that Pharo "does the right, raw, thing" > (at least compared to other mainstream languages), but it still > produces a surprise effect. That's the "floating point surprise" that everyone has at some point, no matter the language and runtime system. If that surprise is a problem for you, are you sure that floating-point arithmetic is what you really want? Maybe your needs are better served with integers and fractions. Konrad.

June 15, 2021

Re: Rounding in Floats

by Esteban Maringolo

On Mon, Jun 14, 2021 at 10:37 PM Richard O'Keefe <raoknz(a)gmail.com> wrote: > For what it's worth, I expected ScaledDecimal to act like fixed point > arithmetic, and implemented it that way in my own Smalltalk library, where > two ScaledDecimals *do* print the same if and only if they are numerically > exactly the same. > What Squeak and Pharo do is exceedingly odd: a ScaledDecimal > is an exact rational number (Integer or Fraction) combined with a precision that > is used for printing, not for calculation. I pointed out before the weird behavior of ScaledDecimals in Pharo, two ScaledDecimal that print the same are not equal. Giving some weird comparison issues as result. > There really isn't any principle of least surprise when it comes to floating- > point arithmetic. It's full of surprises and edge cases. Excel in particular > is notorious for messing up due to trying to pretend all is well. > In this particular case, the exact result is 4.5 Well... for the end user, it produces what they'd expect. So it might mess up, but in a spreadsheet 6.7 - 2.2 should give 4.5. > There are at least three rules for rounding such numbers: rounding out (5), > rounding in (4), and rounding in [banker'salgorithm] (4 here, but 5.5 -> 6). > So you are pushing up against an edge case for exact hand calculation! I implemented a Float>>#roundedHandicap method that does something like the banking algorithm, but rounds positive numbers towards the next integer and negative numbers towards zero. E.g. 0.49 -> 0 0.5 -> 1 -0.5 -> 0 -0.51 -> -1 Nothing uses more than one decimal, so a ScaledDecimal would work but the specification says that it should use all possible precision in intermediate calculations, so I cannot use it. > I think you need to re-express your entire calculation to use exact arithmetic. I really don't know how to do this, any pointers? Nothing is more straightforward than addition and subtraction to me, 6.7 - 2.2 is the simplest it can get. The common formula here is: h * s / 113 + (r - p), but in this particular case s was 113 so it removed the "troubling" part. > That or get agreement on "de minimis non curat lex". I had to search for that expression. Now I know, I agree. Regards, Esteban A. Maringolo > > > On Tue, 15 Jun 2021 at 08:45, Esteban Maringolo <emaringolo(a)gmail.com> wrote: > > > > I'm coming back to this because I've been bitten by these floating > > points things again. > > > > If in Pharo [1] you do: > > a := 6.7 + (32.8 - 35) > > > > It will produce: > > 4.499999999999997 > > > > Which, when rounded, will produce 4. > > > > In other places [2] I do the same simple addition and subtraction it > > produces 4.5, that when rounded will produce 5. > > > > I know now that Pharo doesn't lie to me while other systems do, and > > all that Richard pointed to before. > > > > The issue here is that I'm following some calculation formula that was > > defined in some of the "other" systems, and so when I follow such a > > formula I get these edgy cases where my system produces a different > > output. > > > > In this case the formula is for golf handicap calculations, and it > > caused my system to give 4 instead of 5 to a player, resulting in > > giving the first place to a player other than the one deserved. > > It was no big deal (it's not The Masters), but these cases appear from > > time to time. > > > > Is there any way to "configure" the floating point calculation to > > behave as the "other systems"? > > > > What is the best way to anticipate these situations, am I the only one > > being bitten by these issues? > > > > Thanks in advance for any hints about these problems. > > > > > > Best regards, > > > > [1] Dolphin Smalltalk, JS, Python, Ruby, Dart produces the same output as Pharo. > > [2] VisualWorks, VAST, Excel, VB and all calculators I tried > > > > > > > > Esteban A. Maringolo > > > > On Tue, Sep 8, 2020 at 12:45 AM Esteban Maringolo <emaringolo(a)gmail.com> wrote: > > > > > > On Tue, Sep 8, 2020 at 12:16 AM Richard O'Keefe <raoknz(a)gmail.com> wrote: > > > > > > > > "7.1 roundTo: 0.1 should return 7.1" > > > > You're still not getting it. > > > > > > I was until Konrad explained it. > > > > > > > Binary floating point CANNOT represent either of those numbers. > > > > You seem to be assuming that Pharo is making some mistake. > > > > It isn't. All it is doing is refusing to lie to you. > > > <snip> > > > > The systems that print 7.1 are LYING to you, > > > > and Pharo is not. > > > > > > I'm not assuming a mistake from Pharo, I had a wrong expectation what > > > to get if I round to that precision. > > > I don't know whether other systems lie or simply fulfill user > > > expectations, if you send the #roundTo: to a float, I did expect to > > > get a number with the same precision. > > > That is my expectation as a user. As in the other thread I expected > > > two scaled decimals that are printed equal to also be compared as > > > equal (which they don't). > > > > > > Whether there is a good reason for those behaviors is beyond my > > > current comprehension, but it certainly doesn't follow the "principle > > > of least surprise". > > > > > > In any case, the method proposed by Tomohiro solved my issues. > > > > > > Regards, > > > > > > Esteban A. Maringolo

June 15, 2021

Re: Rounding in Floats

by Richard O'Keefe

It's not quite clear what is happening in the other systems. Here is R > 6.7 + (32.8 - 35) [1] 4.5 > round(6.7 + (32.8 - 35)) [1] 4 The result *is* 4.499999.... but is *printed* as 4.5. Here is Gambit Scheme > (+ 6.7 (- 32.8 35)) 4.499999999999997 > (round (+ 6.7 (- 32.8 35))) 4. Here is astc Smalltalk 6.7 + (32.8 - 35) printOn: Transcript Transcript tab. (6.7 + (32.8 - 35)) rounded printOn: Transcript. Transcript cr. 4.499999999999997 4 And here is Python >>> x = 6.7 + (32.8 - 35) >>> x 4.499999999999997 >>> round(x) 4 For what it's worth, I expected ScaledDecimal to act like fixed point arithmetic, and implemented it that way in my own Smalltalk library, where two ScaledDecimals *do* print the same if and only if they are numerically exactly the same. What Squeak and Pharo do is exceedingly odd: a ScaledDecimal is an exact rational number (Integer or Fraction) combined with a precision that is used for printing, not for calculation. There really isn't any principle of least surprise when it comes to floating- point arithmetic. It's full of surprises and edge cases. Excel in particular is notorious for messing up due to trying to pretend all is well. In this particular case, the exact result is 4.5 There are at least three rules for rounding such numbers: rounding out (5), rounding in (4), and rounding in [banker'salgorithm] (4 here, but 5.5 -> 6). So you are pushing up against an edge case for exact hand calculation! I think you need to re-express your entire calculation to use exact arithmetic. That or get agreement on "de minimis non curat lex". On Tue, 15 Jun 2021 at 08:45, Esteban Maringolo <emaringolo(a)gmail.com> wrote: > > I'm coming back to this because I've been bitten by these floating > points things again. > > If in Pharo [1] you do: > a := 6.7 + (32.8 - 35) > > It will produce: > 4.499999999999997 > > Which, when rounded, will produce 4. > > In other places [2] I do the same simple addition and subtraction it > produces 4.5, that when rounded will produce 5. > > I know now that Pharo doesn't lie to me while other systems do, and > all that Richard pointed to before. > > The issue here is that I'm following some calculation formula that was > defined in some of the "other" systems, and so when I follow such a > formula I get these edgy cases where my system produces a different > output. > > In this case the formula is for golf handicap calculations, and it > caused my system to give 4 instead of 5 to a player, resulting in > giving the first place to a player other than the one deserved. > It was no big deal (it's not The Masters), but these cases appear from > time to time. > > Is there any way to "configure" the floating point calculation to > behave as the "other systems"? > > What is the best way to anticipate these situations, am I the only one > being bitten by these issues? > > Thanks in advance for any hints about these problems. > > > Best regards, > > [1] Dolphin Smalltalk, JS, Python, Ruby, Dart produces the same output as Pharo. > [2] VisualWorks, VAST, Excel, VB and all calculators I tried > > > > Esteban A. Maringolo > > On Tue, Sep 8, 2020 at 12:45 AM Esteban Maringolo <emaringolo(a)gmail.com> wrote: > > > > On Tue, Sep 8, 2020 at 12:16 AM Richard O'Keefe <raoknz(a)gmail.com> wrote: > > > > > > "7.1 roundTo: 0.1 should return 7.1" > > > You're still not getting it. > > > > I was until Konrad explained it. > > > > > Binary floating point CANNOT represent either of those numbers. > > > You seem to be assuming that Pharo is making some mistake. > > > It isn't. All it is doing is refusing to lie to you. > > <snip> > > > The systems that print 7.1 are LYING to you, > > > and Pharo is not. > > > > I'm not assuming a mistake from Pharo, I had a wrong expectation what > > to get if I round to that precision. > > I don't know whether other systems lie or simply fulfill user > > expectations, if you send the #roundTo: to a float, I did expect to > > get a number with the same precision. > > That is my expectation as a user. As in the other thread I expected > > two scaled decimals that are printed equal to also be compared as > > equal (which they don't). > > > > Whether there is a good reason for those behaviors is beyond my > > current comprehension, but it certainly doesn't follow the "principle > > of least surprise". > > > > In any case, the method proposed by Tomohiro solved my issues. > > > > Regards, > > > > Esteban A. Maringolo

June 15, 2021

Re: Rounding in Floats

by Esteban Maringolo

Hi Sven, > > If in Pharo [1] you do: > > a := 6.7 + (32.8 - 35) > > It will produce: > > 4.499999999999997 > > Which, when rounded, will produce 4. > But, > a roundTo: 0.1 "=> 4.5" Sure, but what initiated this thread was a reference to roundTo: 0.1 which produced a "wrong" output. (9.1 + (-2.0)) roundTo: 0.1 "=> 7.1000000000000005" 7.1 roundTo: 0.1 "=> 7.1000000000000005" However, at this point I know that Pharo "does the right, raw, thing" (at least compared to other mainstream languages), but it still produces a surprise effect. In particular when people go to Excel to "check that your system does the right thing", uses the same formula and it gives a different result to them. Then open a calculator (or a physical one) and it gives the same number as Excel. So an hour after the fact you're arguing about floating point implementations to non-technical people :-) Regards! Esteban A. Maringolo

June 14, 2021

Re: Rounding in Floats

by Sven Van Caekenberghe

BTW, I recently wrote my own float printer, as an experiment. NeoJSONFloatPrinter lowPrecision print: a. => 4.5 What I wanted was a human friendly, compact float printer, that tries to go for the shortest, simplest number. It prefers integers and goes to scientific notation when needed, while limiting the precision. Maybe it is interesting to look at the code. But I am far from an expert. > On 14 Jun 2021, at 23:23, Sven Van Caekenberghe <sven(a)stfx.eu> wrote: > > > >> On 14 Jun 2021, at 22:44, Esteban Maringolo <emaringolo(a)gmail.com> wrote: >> >> I'm coming back to this because I've been bitten by these floating >> points things again. >> >> If in Pharo [1] you do: >> a := 6.7 + (32.8 - 35) >> >> It will produce: >> 4.499999999999997 >> >> Which, when rounded, will produce 4. > > But, > > a roundTo: 0.1 "=> 4.5" > >> In other places [2] I do the same simple addition and subtraction it >> produces 4.5, that when rounded will produce 5. >> >> I know now that Pharo doesn't lie to me while other systems do, and >> all that Richard pointed to before. >> >> The issue here is that I'm following some calculation formula that was >> defined in some of the "other" systems, and so when I follow such a >> formula I get these edgy cases where my system produces a different >> output. >> >> In this case the formula is for golf handicap calculations, and it >> caused my system to give 4 instead of 5 to a player, resulting in >> giving the first place to a player other than the one deserved. >> It was no big deal (it's not The Masters), but these cases appear from >> time to time. >> >> Is there any way to "configure" the floating point calculation to >> behave as the "other systems"? >> >> What is the best way to anticipate these situations, am I the only one >> being bitten by these issues? >> >> Thanks in advance for any hints about these problems. >> >> >> Best regards, >> >> [1] Dolphin Smalltalk, JS, Python, Ruby, Dart produces the same output as Pharo. >> [2] VisualWorks, VAST, Excel, VB and all calculators I tried >> >> >> >> Esteban A. Maringolo >> >> On Tue, Sep 8, 2020 at 12:45 AM Esteban Maringolo <emaringolo(a)gmail.com> wrote: >>> >>> On Tue, Sep 8, 2020 at 12:16 AM Richard O'Keefe <raoknz(a)gmail.com> wrote: >>>> >>>> "7.1 roundTo: 0.1 should return 7.1" >>>> You're still not getting it. >>> >>> I was until Konrad explained it. >>> >>>> Binary floating point CANNOT represent either of those numbers. >>>> You seem to be assuming that Pharo is making some mistake. >>>> It isn't. All it is doing is refusing to lie to you. >>> <snip> >>>> The systems that print 7.1 are LYING to you, >>>> and Pharo is not. >>> >>> I'm not assuming a mistake from Pharo, I had a wrong expectation what >>> to get if I round to that precision. >>> I don't know whether other systems lie or simply fulfill user >>> expectations, if you send the #roundTo: to a float, I did expect to >>> get a number with the same precision. >>> That is my expectation as a user. As in the other thread I expected >>> two scaled decimals that are printed equal to also be compared as >>> equal (which they don't). >>> >>> Whether there is a good reason for those behaviors is beyond my >>> current comprehension, but it certainly doesn't follow the "principle >>> of least surprise". >>> >>> In any case, the method proposed by Tomohiro solved my issues. >>> >>> Regards, >>> >>> Esteban A. Maringolo

June 14, 2021

Re: Rounding in Floats

by Sven Van Caekenberghe

> On 14 Jun 2021, at 22:44, Esteban Maringolo <emaringolo(a)gmail.com> wrote: > > I'm coming back to this because I've been bitten by these floating > points things again. > > If in Pharo [1] you do: > a := 6.7 + (32.8 - 35) > > It will produce: > 4.499999999999997 > > Which, when rounded, will produce 4. But, a roundTo: 0.1 "=> 4.5" > In other places [2] I do the same simple addition and subtraction it > produces 4.5, that when rounded will produce 5. > > I know now that Pharo doesn't lie to me while other systems do, and > all that Richard pointed to before. > > The issue here is that I'm following some calculation formula that was > defined in some of the "other" systems, and so when I follow such a > formula I get these edgy cases where my system produces a different > output. > > In this case the formula is for golf handicap calculations, and it > caused my system to give 4 instead of 5 to a player, resulting in > giving the first place to a player other than the one deserved. > It was no big deal (it's not The Masters), but these cases appear from > time to time. > > Is there any way to "configure" the floating point calculation to > behave as the "other systems"? > > What is the best way to anticipate these situations, am I the only one > being bitten by these issues? > > Thanks in advance for any hints about these problems. > > > Best regards, > > [1] Dolphin Smalltalk, JS, Python, Ruby, Dart produces the same output as Pharo. > [2] VisualWorks, VAST, Excel, VB and all calculators I tried > > > > Esteban A. Maringolo > > On Tue, Sep 8, 2020 at 12:45 AM Esteban Maringolo <emaringolo(a)gmail.com> wrote: >> >> On Tue, Sep 8, 2020 at 12:16 AM Richard O'Keefe <raoknz(a)gmail.com> wrote: >>> >>> "7.1 roundTo: 0.1 should return 7.1" >>> You're still not getting it. >> >> I was until Konrad explained it. >> >>> Binary floating point CANNOT represent either of those numbers. >>> You seem to be assuming that Pharo is making some mistake. >>> It isn't. All it is doing is refusing to lie to you. >> <snip> >>> The systems that print 7.1 are LYING to you, >>> and Pharo is not. >> >> I'm not assuming a mistake from Pharo, I had a wrong expectation what >> to get if I round to that precision. >> I don't know whether other systems lie or simply fulfill user >> expectations, if you send the #roundTo: to a float, I did expect to >> get a number with the same precision. >> That is my expectation as a user. As in the other thread I expected >> two scaled decimals that are printed equal to also be compared as >> equal (which they don't). >> >> Whether there is a good reason for those behaviors is beyond my >> current comprehension, but it certainly doesn't follow the "principle >> of least surprise". >> >> In any case, the method proposed by Tomohiro solved my issues. >> >> Regards, >> >> Esteban A. Maringolo

June 14, 2021

Re: Rounding in Floats

by Esteban Maringolo

I'm coming back to this because I've been bitten by these floating points things again. If in Pharo [1] you do: a := 6.7 + (32.8 - 35) It will produce: 4.499999999999997 Which, when rounded, will produce 4. In other places [2] I do the same simple addition and subtraction it produces 4.5, that when rounded will produce 5. I know now that Pharo doesn't lie to me while other systems do, and all that Richard pointed to before. The issue here is that I'm following some calculation formula that was defined in some of the "other" systems, and so when I follow such a formula I get these edgy cases where my system produces a different output. In this case the formula is for golf handicap calculations, and it caused my system to give 4 instead of 5 to a player, resulting in giving the first place to a player other than the one deserved. It was no big deal (it's not The Masters), but these cases appear from time to time. Is there any way to "configure" the floating point calculation to behave as the "other systems"? What is the best way to anticipate these situations, am I the only one being bitten by these issues? Thanks in advance for any hints about these problems. Best regards, [1] Dolphin Smalltalk, JS, Python, Ruby, Dart produces the same output as Pharo. [2] VisualWorks, VAST, Excel, VB and all calculators I tried Esteban A. Maringolo On Tue, Sep 8, 2020 at 12:45 AM Esteban Maringolo <emaringolo(a)gmail.com> wrote: > > On Tue, Sep 8, 2020 at 12:16 AM Richard O'Keefe <raoknz(a)gmail.com> wrote: > > > > "7.1 roundTo: 0.1 should return 7.1" > > You're still not getting it. > > I was until Konrad explained it. > > > Binary floating point CANNOT represent either of those numbers. > > You seem to be assuming that Pharo is making some mistake. > > It isn't. All it is doing is refusing to lie to you. > <snip> > > The systems that print 7.1 are LYING to you, > > and Pharo is not. > > I'm not assuming a mistake from Pharo, I had a wrong expectation what > to get if I round to that precision. > I don't know whether other systems lie or simply fulfill user > expectations, if you send the #roundTo: to a float, I did expect to > get a number with the same precision. > That is my expectation as a user. As in the other thread I expected > two scaled decimals that are printed equal to also be compared as > equal (which they don't). > > Whether there is a good reason for those behaviors is beyond my > current comprehension, but it certainly doesn't follow the "principle > of least surprise". > > In any case, the method proposed by Tomohiro solved my issues. > > Regards, > > Esteban A. Maringolo

June 14, 2021

[ANN] Hyperspace v2.8.0 [v2.8.0] released!

by Buenos Aires Smalltalk

June 14, 2021

Re: [ANN] Pharo-ODBC

by Esteban Maringolo

Thank you John! This is very good news! Best regards, Esteban A. Maringolo On Mon, Jun 14, 2021 at 6:29 AM John Aspinall <john.aspinall(a)gmail.com> wrote: > > There is now an ODBC framework for Pharo, available at the pharo-rdbms github site: > > https://github.com/pharo-rdbms/Pharo-ODBC > > This is based on the Dolphin Smalltalk Database Connection ODBC framework. Provided a suitable driver manager is installed this should work on MacOS and Linux in addition to Windows. > > Thanks to InfOil for supporting the development, to Torsten for tidying up and hosting the code, and Andy and Blair (Dolphin developers) for the original framework. > > Regards, > > John Aspinall

June 14, 2021