Re: The 'Value' of Basic Maths (was: Basic Maths)
Jacqueline Landman Gay a écrit : > > > Original conundrum... > > > > >Type this in the message box... > > >put 5.45 - 4 = 1.45 FALSE > > > > I am getting flak on the HyperCard mailing list for mentioning MetaCard, > so I suppose I may as well round out my career by mentioning that > HyperCard does this math just fine, no errors. So there must be a way > around it; maybe it's a MetaCard thing. > > -- > Jacqueline Landman Gay | [EMAIL PROTECTED] > HyperActive Software | 612-724-1596 > Custom hypermedia solutions| http://www.hyperactivesw.com > > Archives: http://www.mail-archive.com/metacard@lists.runrev.com/ > Info: http://www.xworlds.com/metacard/mailinglist.htm > Please send bug reports to <[EMAIL PROTECTED]>, not this list. Don't worry Jacque... integrists are ever and ever stored in theyr integrism close boxes :-) We are lots to remember what you did for and with hc. Kind Regards, Pierre Sahores WEB & VPN applications and databases servers Inspection académique de la Seine-Saint-Denis Penser la part du rêve et produire l'avantage Archives: http://www.mail-archive.com/metacard@lists.runrev.com/ Info: http://www.xworlds.com/metacard/mailinglist.htm Please send bug reports to <[EMAIL PROTECTED]>, not this list.
Re: The 'Value' of Basic Maths (was: Basic Maths)
> Original conundrum... > > >Type this in the message box... > >put 5.45 - 4 = 1.45 FALSE > I am getting flak on the HyperCard mailing list for mentioning MetaCard, so I suppose I may as well round out my career by mentioning that HyperCard does this math just fine, no errors. So there must be a way around it; maybe it's a MetaCard thing. -- Jacqueline Landman Gay | [EMAIL PROTECTED] HyperActive Software | 612-724-1596 Custom hypermedia solutions| http://www.hyperactivesw.com Archives: http://www.mail-archive.com/metacard@lists.runrev.com/ Info: http://www.xworlds.com/metacard/mailinglist.htm Please send bug reports to <[EMAIL PROTECTED]>, not this list.
The 'Value' of Basic Maths (was: Basic Maths)
Original conundrum... >Type this in the message box... >put 5.45 - 4 = 1.45 FALSE So we have a sever dose of the floating point accuracies, huh John? >On the surface, it appears to me that this is an interesting example of how >roundoff errors in computer calculations can cause programming headaches if >your logic is testing for absolute equality. Claude agrees: >As a workaround you can use round(myNumber,nDigits) > >put round((5.45-4),10)-round((1.45),10)=0 TRUE John's observation below hints at a curious solution, however... >The moral of the story is to never build logic into numerical programs >that relies on recognizing precise equality of two floating point numbers. put VALUE(5.45 - 4) = 1.45 TRUE Presumably, 'value' applies a different set of rules. At least I have a solution for my accounts validation check, but I do feel a computer should manage basic subtraction. There was a discussion about this a while ago, essentially explaining how computers behave this way. No-one to the best of my recollection actually explained why they have to, however. The moral of this story is to remember your values. /H Hugh Senior The Flexible Learning Company Consultant Programming & Software Solutions Fax/Voice: +44 (0)1483.27 87 27 Email: [EMAIL PROTECTED] Web: www.flexibleLearning.com Archives: http://www.mail-archive.com/metacard@lists.runrev.com/ Info: http://www.xworlds.com/metacard/mailinglist.htm Please send bug reports to <[EMAIL PROTECTED]>, not this list.
Re: Basic Maths
Hugh Senior wrote : > put 5.45 - 3 = 2.45 TRUE > but... > put 5.45 - 4 = 1.45 FALSE Same bug on my Pentium based computer. Even put 5.45 - 4.0 = 1.45 FALSE Pentium's or mc's bug ? As a workaround you can use round(myNumber,nDigits) put round((5.45-4),10)-round((1.45),10)=0 TRUE Claude Archives: http://www.mail-archive.com/metacard@lists.runrev.com/ Info: http://www.xworlds.com/metacard/mailinglist.htm Please send bug reports to <[EMAIL PROTECTED]>, not this list.
Re: Basic Maths
Hugh Senior wrote: >Type this in the message box... > >put 5.45 - 1 = 4.45 TRUE >put 5.45 - 2 = 3.45 TRUE >put 5.45 - 3 = 2.45 TRUE > >but... > >put 5.45 - 4 = 1.45 FALSE > >Huh? This is not helping my sanity, nor writing a finance checking routine >that answers false instead of true! > >Any answers out there? On the surface, it appears to me that this is an interesting example of how roundoff errors in computer calculations can cause programming headaches if your logic is testing for absolute equality. As a further test, I did the subtractions Hugh did, and then went on to substract the supposed difference, which logically ought to produce 0. The tests worked out this way: put (5.45 - 1) - 4.45 = 0 TRUE put (5.45 - 2) - 3.45 = 0 TRUE put (5.45 - 3) - 2.45 = 0 TRUE put (5.45 - 4) - 1.45 = 0 FALSE These results are consistent with Hugh's. Now focussing on the last case, let us test this differece which ought to be equal to zero but which the computer says is not zero to see how small the computer agrees that it is in absolute value. These were my results with MetaCard: put abs((5.45 - 4) - 1.45) < 0.0001 FALSE put abs((5.45 - 4) - 1.45) < 0.001 TRUE Thus, it appears that the roundoff error that occurs when substracting 4 from 5.45, and then further subtracting 1.45 from that is in the 16th decimal place. The moral of the story is to never build logic into numberical programs that relies on recognizing precise equality of two floating point numbers. You can count on precision, however, with integer arithmetic, provided you do not get so large as to produce overflow errors. For example, if we multiply Hugh's example by 100 to get all the numbers being integers, MetaCard says: put 545 - 400 = 145 TRUE Pardon me if this may be more detailed than some readers of this list may care to see. It's the math prof in me. Since this is my first post, let me introduce myself. I am a professor of mathematics at Northern Michigan University. I am interested in MetaCard because it is allowing me to upgrade and make more broadly available some permutation puzzles that I developed in HyperCard for use in teaching one of my courses some years ago. I ported them over to MetaCard over a year ago, and did some improvements on them at the time. Now I am doing a more intensive upgrade. I have found reading this list to be very helpful over the past year that I have been getting it. Now that I am getting more into working with MetaCard, you may hear from me with questions from time to time. Don't look for answers from here that have to do with the hard core computer programming, however. I am a reluctant programmer, doing it only when I have a project that wouldn't get done otherwise. John Kiltinen John Kiltinen ([EMAIL PROTECTED])Home Office Professor, Dept. of Math. & CS Tel.(906) 228-8035 or (906) 227-1600 Northern Michigan University Fax (906) 228-4667 or (906) 2272010 Marquette, MI 49855 USA Archives: http://www.mail-archive.com/metacard@lists.runrev.com/ Info: http://www.xworlds.com/metacard/mailinglist.htm Please send bug reports to <[EMAIL PROTECTED]>, not this list.
Basic Maths
Type this in the message box... put 5.45 - 1 = 4.45 TRUE put 5.45 - 2 = 3.45 TRUE put 5.45 - 3 = 2.45 TRUE but... put 5.45 - 4 = 1.45 FALSE Huh? This is not helping my sanity, nor writing a finance checking routine that answers false instead of true! Any answers out there? /H Hugh Senior The Flexible Learning Company Consultant Programming & Software Solutions Fax/Voice: +44 (0)1483.27 87 27 Email: [EMAIL PROTECTED] Web: www.flexibleLearning.com Archives: http://www.mail-archive.com/metacard@lists.runrev.com/ Info: http://www.xworlds.com/metacard/mailinglist.htm Please send bug reports to <[EMAIL PROTECTED]>, not this list.
