January 2020 - Pharo-users - lists.pharo.org

Re: [Pharo-users] Floating point arithmetic

by Sven Van Caekenberghe

> On 13 Jan 2020, at 00:28, Paul DeBruicker <pdebruic(a)gmail.com> wrote: > > Whats wrong with #roundedTo: ? > > > If you actually need it calculated to 8 significant digits then you can use > scaled decimals e.g. > > (0.09560268 asScaledDecimal - 0.005 asScaledDecimal) The weird thing is though, that is still does not behave 100% as one would expect (i.e. it does not seem exact). 0.09560268 asScaledDecimal - 0.005 asScaledDecimal. "0.09060268s8" 0.09560268 asScaledDecimal - 0.005 asScaledDecimal = 0.09060268 asScaledDecimal. "false" 0.09560268 asScaledDecimal - 0.005 asScaledDecimal = 0.09060268s8. "false" The internal fractions are not the same ... While (9560268 / 1e8) - (5 / 1e3) = (9060268 / 1e8). "true" So, is the equality test of ScaledDecimal correct ? > see https://0.30000000000000004.com for more about why floating point math > does this sometimes > > > > > > Donald Howard wrote >> Hello everyone, >> >> This is an issue I've had awareness of going way back but it's the first >> time I've had to personally deal with it. I've done some research and >> found it addressed in a number of ways but given current time pressures >> and >> a huge list of to-dos, I thought I'd turn to the community for rapid >> advice >> to get me over the hump. The circumstances are summarized below in code >> and comments suitable for a playground. >> >> "This is the actual arithmetic I want to do... >> 0.09560268 - 0.005 = 0.09060268" >> >> "Evaluate this in a playground and you'll see this is what >> floating point arithmetic produces --the first two are wrong, every one >> after is correct" >> 0.09560268 - 0.005 "=> 0.09060267999999999". >> 0.0956026 - 0.005 "=> 0.09060259999999999". >> 0.095602 - 0.005 "=> 0.090602". >> 0.09560 - 0.005 "=> 0.0906". >> 0.0956 - 0.005 "=> 0.0906". >> 0.095 - 0.005 "=> 0.09". >> >> "This workaround works" >> 0.09560268 - 0.005 roundTo: 0.00000001 "=> 0.09060268". >> "but one has to compute number of digits of precision >> and according to study above, it's not necessary at >> precisions >= 0.000001" >> >> "What are other suggestions, workarounds or approaches community has?" >> "THANKS!" >> >> >> Don Howard >> >> <https://objectguild.com> >> *Founding Member* > >> dhoward@ > >> +31653139744 >> (US) 651-253-7024 > > > > > > -- > Sent from: http://forum.world.st/Pharo-Smalltalk-Users-f1310670.html

Jan. 13, 2020

Re: [Pharo-users] Floating point arithmetic

by Ben Coman

On Mon, 13 Jan 2020 at 19:42, Richard O'Keefe <raoknz(a)gmail.com> wrote: > You say that the first two results are wrong. > No. The first two results are *exactly* what they are supposed to be. > Floating point arithmetic is NOT mathematical real arithmetic. > The floating point *numbers* are exact rational numbers of the form > n * 2^k where n is a (bounded) integer and k is a (bounded) integer. > If you enter a number that is not of this form (and within bounds) > you will get a *different* number that *is* of that form and is close. > The floating point *operations* in IEEE arithmetic are exact > when and only when the result is a number of that form (and within > bounds), otherwise the result is *approximate*. > > If you want exact arithmetic on numbers of the form n * 10^k, > ANSI Smalltalk provides the ScaledDecimal class, which, sigh, > How could this be improved? > Squeak and Pharo interpret as "rational number *printed* in > decimal form but not *computed* using decimal arithmetic" > I'm interested to understand what is the benefit of doing it this way. Anyone know history of it? cheers -ben , so > that can give extremely confusing results too. > > So what you are going to have to do is use rational numbers, > which are in Smalltalk the union of Integer and Fraction. > > > On Mon, 13 Jan 2020 at 09:13, Donald Howard <dhoward(a)objectguild.com> > wrote: > >> Hello everyone, >> >> This is an issue I've had awareness of going way back but it's the first >> time I've had to personally deal with it. I've done some research and >> found it addressed in a number of ways but given current time pressures and >> a huge list of to-dos, I thought I'd turn to the community for rapid advice >> to get me over the hump. The circumstances are summarized below in code >> and comments suitable for a playground. >> >> "This is the actual arithmetic I want to do... >> 0.09560268 - 0.005 = 0.09060268" >> >> "Evaluate this in a playground and you'll see this is what >> floating point arithmetic produces --the first two are wrong, every one >> after is correct" >> 0.09560268 - 0.005 "=> 0.09060267999999999". >> 0.0956026 - 0.005 "=> 0.09060259999999999". >> 0.095602 - 0.005 "=> 0.090602". >> 0.09560 - 0.005 "=> 0.0906". >> 0.0956 - 0.005 "=> 0.0906". >> 0.095 - 0.005 "=> 0.09". >> >> "This workaround works" >> 0.09560268 - 0.005 roundTo: 0.00000001 "=> 0.09060268". >> "but one has to compute number of digits of precision >> and according to study above, it's not necessary at >> precisions >= 0.000001" >> >> "What are other suggestions, workarounds or approaches community has?" >> "THANKS!" >> >> >> Don Howard >> >> <https://objectguild.com> >> *Founding Member* >> dhoward(a)objectguild.com >> +31653139744 >> (US) 651-253-7024 >> >

Jan. 13, 2020

Re: [Pharo-users] As promised, the sequel!

by xap

Richard, another entertaining smalltalk read; thx :) If when you wrote the prequel you hadn't already meant to follow up w/ the e-car parallel, perhaps refer to this mailing list and attendant discussion and tbrunz' specific comments here: http://forum.world.st/Smalltalk-It-s-Not-Your-Grandfather-s-Programming-Lan… ? -- Sent from: http://forum.world.st/Pharo-Smalltalk-Users-f1310670.html

Jan. 13, 2020

Re: [Pharo-users] Floating point arithmetic

by Richard O'Keefe

You say that the first two results are wrong. No. The first two results are *exactly* what they are supposed to be. Floating point arithmetic is NOT mathematical real arithmetic. The floating point *numbers* are exact rational numbers of the form n * 2^k where n is a (bounded) integer and k is a (bounded) integer. If you enter a number that is not of this form (and within bounds) you will get a *different* number that *is* of that form and is close. The floating point *operations* in IEEE arithmetic are exact when and only when the result is a number of that form (and within bounds), otherwise the result is *approximate*. If you want exact arithmetic on numbers of the form n * 10^k, ANSI Smalltalk provides the ScaledDecimal class, which, sigh, Squeak and Pharo interpret as "rational number *printed* in decimal form but not *computed* using decimal arithmetic", so that can give extremely confusing results too. So what you are going to have to do is use rational numbers, which are in Smalltalk the union of Integer and Fraction. On Mon, 13 Jan 2020 at 09:13, Donald Howard <dhoward(a)objectguild.com> wrote: > Hello everyone, > > This is an issue I've had awareness of going way back but it's the first > time I've had to personally deal with it. I've done some research and > found it addressed in a number of ways but given current time pressures and > a huge list of to-dos, I thought I'd turn to the community for rapid advice > to get me over the hump. The circumstances are summarized below in code > and comments suitable for a playground. > > "This is the actual arithmetic I want to do... > 0.09560268 - 0.005 = 0.09060268" > > "Evaluate this in a playground and you'll see this is what > floating point arithmetic produces --the first two are wrong, every one > after is correct" > 0.09560268 - 0.005 "=> 0.09060267999999999". > 0.0956026 - 0.005 "=> 0.09060259999999999". > 0.095602 - 0.005 "=> 0.090602". > 0.09560 - 0.005 "=> 0.0906". > 0.0956 - 0.005 "=> 0.0906". > 0.095 - 0.005 "=> 0.09". > > "This workaround works" > 0.09560268 - 0.005 roundTo: 0.00000001 "=> 0.09060268". > "but one has to compute number of digits of precision > and according to study above, it's not necessary at > precisions >= 0.000001" > > "What are other suggestions, workarounds or approaches community has?" > "THANKS!" > > > Don Howard > > <https://objectguild.com> > *Founding Member* > dhoward(a)objectguild.com > +31653139744 > (US) 651-253-7024 >

Jan. 13, 2020

Re: [Pharo-users] Floating point arithmetic

by Konrad Hinsen

On 12/01/2020 21:13, Donald Howard wrote: > "Evaluate this in a playground and you'll see this is what > Â floating point arithmetic produces --the first two are wrong, every > one after is correct" > 0.09560268 - 0.005 "=> 0.09060267999999999". > 0.0956026 - 0.005 Â "=> 0.09060259999999999". > 0.095602 - 0.005 Â "=> 0.090602". Wrong in what sense? I am rather sure that the computation is done correctly, meaning that it follows the rules defined by IEEE standard 754. I am also relatively sure (meaning a bit less) that the conversion of the binary result to a decimal output string is correct, in the sense that it applies today's preferred practice of ensuring round-trip equality. So you probably mean that the result is no what you expected. The main point to be clear about is if you care about the binary value or about its decimal representation as a string. If you need the internal value to be exact, you have to switch to something other than binary floats - scaled decimals might work for you. If you only want nice-looking outputs, you can probably get what you want using roundTo: applied to the result. Cheers, Konrad.

Jan. 13, 2020

As promised, the sequel!

by Richard Kenneth Eng

https://levelup.gitconnected.com/how-is-smalltalks-revival-like-the-e-car-s…

Jan. 13, 2020

Re: [Pharo-users] Floating point arithmetic

by Paul DeBruicker

Whats wrong with #roundedTo: ? If you actually need it calculated to 8 significant digits then you can use scaled decimals e.g. (0.09560268 asScaledDecimal - 0.005 asScaledDecimal) see https://0.30000000000000004.com for more about why floating point math does this sometimes Donald Howard wrote > Hello everyone, > > This is an issue I've had awareness of going way back but it's the first > time I've had to personally deal with it. I've done some research and > found it addressed in a number of ways but given current time pressures > and > a huge list of to-dos, I thought I'd turn to the community for rapid > advice > to get me over the hump. The circumstances are summarized below in code > and comments suitable for a playground. > > "This is the actual arithmetic I want to do... > 0.09560268 - 0.005 = 0.09060268" > > "Evaluate this in a playground and you'll see this is what > floating point arithmetic produces --the first two are wrong, every one > after is correct" > 0.09560268 - 0.005 "=> 0.09060267999999999". > 0.0956026 - 0.005 "=> 0.09060259999999999". > 0.095602 - 0.005 "=> 0.090602". > 0.09560 - 0.005 "=> 0.0906". > 0.0956 - 0.005 "=> 0.0906". > 0.095 - 0.005 "=> 0.09". > > "This workaround works" > 0.09560268 - 0.005 roundTo: 0.00000001 "=> 0.09060268". > "but one has to compute number of digits of precision > and according to study above, it's not necessary at > precisions >= 0.000001" > > "What are other suggestions, workarounds or approaches community has?" > "THANKS!" > > > Don Howard > > <https://objectguild.com> > *Founding Member* > dhoward@ > +31653139744 > (US) 651-253-7024 -- Sent from: http://forum.world.st/Pharo-Smalltalk-Users-f1310670.html

Jan. 12, 2020

Floating point arithmetic

by Donald Howard

Hello everyone, This is an issue I've had awareness of going way back but it's the first time I've had to personally deal with it. I've done some research and found it addressed in a number of ways but given current time pressures and a huge list of to-dos, I thought I'd turn to the community for rapid advice to get me over the hump. The circumstances are summarized below in code and comments suitable for a playground. "This is the actual arithmetic I want to do... 0.09560268 - 0.005 = 0.09060268" "Evaluate this in a playground and you'll see this is what floating point arithmetic produces --the first two are wrong, every one after is correct" 0.09560268 - 0.005 "=> 0.09060267999999999". 0.0956026 - 0.005 "=> 0.09060259999999999". 0.095602 - 0.005 "=> 0.090602". 0.09560 - 0.005 "=> 0.0906". 0.0956 - 0.005 "=> 0.0906". 0.095 - 0.005 "=> 0.09". "This workaround works" 0.09560268 - 0.005 roundTo: 0.00000001 "=> 0.09060268". "but one has to compute number of digits of precision and according to study above, it's not necessary at precisions >= 0.000001" "What are other suggestions, workarounds or approaches community has?" "THANKS!" Don Howard <https://objectguild.com> *Founding Member* dhoward(a)objectguild.com +31653139744 (US) 651-253-7024

Jan. 12, 2020

Re: [Pharo-users] Pharo on OpenSUSE (FFI / libgit2 errors)

by Jan BlizniÄenko

So it seems the good old ln -s /usr/lib64/libcurl.so.4 (path to pharo)/pharo-vm/lib/pharo/(version)/libcurl-gnutls.so.4 still works after all, just not with Pharo Launcher VM (where it causes segfault). With regular VMs downloaded either manually or via the Launcher itself it works. Too bad it makes Launcher unusable on both systems for both reasons (cannot hotfix launcher itself and have to hotfix all VMs it downloads). Jan -- Sent from: http://forum.world.st/Pharo-Smalltalk-Users-f1310670.html

Jan. 12, 2020

Re: [Pharo-users] Pharo on OpenSUSE (FFI / libgit2 errors)

by Jan BlizniÄenko

Hello Thank you for this script. Unfortunately it does not seem to work for me. After downloading that VM you linked and downloaded image with sources, image opens and immediately crashes: ioLoadModule(//home/honza/Downloads/pharo64-linux-stable/lib/pharo/5.0-201902062351/libgit2.so): /usr/lib64/libgnutls.so.30: symbol nettle_rsa_pss_sha384_sign_digest_tr, version HOGWEED_4 not defined in file libhogweed.so.4 with link time reference External module not found ExternalLibraryFunction(Object)>>error: ExternalLibraryFunction(Object)>>externalCallFailed ExternalLibraryFunction(ExternalFunction)>>invokeWithArguments: LGitLibrary>>libgit2_init FFICalloutAPI>>function:library: LGitLibrary(Object)>>ffiCall:library:options: During execution of the script, there are these suspicious lines exactly repeated for each of the 6 add_dependencies call (so 6 times in whole script): + tar -xv --strip-components=3 -C lib/pharo/5.0-201902062351 -f data.tar.xz ./lib/x86_64-linux-gnu tar: ./lib/x86_64-linux-gnu: Not found in archive tar: Exiting with failure status due to previous errors Jan -- Sent from: http://forum.world.st/Pharo-Smalltalk-Users-f1310670.html

Jan. 12, 2020