Thank you Stuart and Happy Thanksgiving! Doug
-sent from mobile- > On Nov 26, 2019, at 11:53 PM, Raeburn, Stuart <raeb...@msu.edu> wrote: > > Doug, > > Borrowing from the fp_equal() subroutine used to compare whether two > floating-point numbers are equal, to a particular number of decimal places, > found at: > http://perldoc.perl.org/perlop.html#Floating-point-Arithmetic > > you could test whether the values of $molt4 and $actualM rounded to the > desired precision (e.g., 3 decimal places) are the same, and if so, set the > $percenterror to 0, otherwise calculate $percenterror, using the method you > used in your example. > > $precision = 3; > if (&roundto($molt4,$precision) eq &roundto($actualM,$precision)) { > $percenterror = 0; > } else { > $percenterror=abs($molt4-$actualM)*100/$actualM; > } > > For any user supplied input you should also validate that the experimental > data are reasonable. Note: you could also set an absolute tolerance for the > case where the $percenterror is 0, and use a relative tolerance otherwise. > (Note: any tolerance defined within the problem could be overridden within a > course). > > if (&roundto($molt4,$precision) eq &roundto($actualM,$precision)) { > $temp = 0; > $percenterror = 0; > $tol = 0.1; > } else { > $tol = '5%'; > $temp = $molt4-$actualM; > $percenterror=abs($molt4-$actualM)*100/$actualM; > } > > <numericalresponse format="3s" answer="$percenterror" id="11"> > <responseparam name="tol" type="tolerance" default="$tol" > description="Numerical Tolerance" /> > <responseparam name="sig" type="int_range" default="3,4" > description="Significant Digits" /> > <textline readonly="no" /> > </numericalresponse> > > Stuart Raeburn > LON-CAPA Academic Consortium > > ________________________________________ > From: LON-CAPA-users <lon-capa-users-boun...@mail.lon-capa.org> on behalf of > Mills, Douglas G <dmi...@illinois.edu> > Sent: Tuesday, November 26, 2019 4:55 PM > To: Discussion list for LON-CAPA users > Cc: Mills, Douglas G > Subject: [LON-CAPA-users] How Best to Resolve Floating Point Issues? > > Hi All, > > I've run into a situation where the binary representation of base 10 numbers > is catching up to us for a very small percentage of our students. To > illustrate this I've created a public problem demonstrating the issue. Unlike > the problems the students get this one, for the sake of demonstration, walks > you through the calculations but uses the exact same numbers that one of our > students had to work with resulting in a case where what should be zero is > not equal to zero. What's the best way of preventing this from happening? > (The source code is open also in case you want to have a look but it's pretty > well spelled out in the problem itself for demonstration purposes). > > https://access3.lon-capa.illinois.edu/res/uiuc/dmills/scratchwork/FloatingPointIssueDemo.problem<https://urldefense.com/v3/__https://access3.lon-capa.illinois.edu/res/uiuc/dmills/scratchwork/FloatingPointIssueDemo.problem__;!ioFpBMP7lJU!kYg_ctrV6fkf5-Q0k15HPZw7eDzJHG_oXmJmgLbFYGCVB4UljJ9noqPl_BVJGg$> > > Thanks in advance and, on that topic, Happy Thanksgiving! > > Doug > > DOUGLAS G MILLS > Director of Instructional Technology > > Department of Chemistry > > University of Illinois at Urbana-Champaign > Chemistry Annex Box A2 > 601 S. Mathews | M/C 712 > Urbana, IL 61801 > 217.244.5739 | fax: 217.244.8029 | > dmi...@illinois.edu<mailto:dmi...@illinois.edu> > chemistry.illinois.edu<https://urldefense.com/v3/__http://chemistry.illinois.edu__;!ioFpBMP7lJU!kYg_ctrV6fkf5-Q0k15HPZw7eDzJHG_oXmJmgLbFYGCVB4UljJ9noqMWvh09LQ$> > > [/var/folders/kv/f3wpy1cs51521x5grm_qx4tw0000gn/T/com.microsoft.Outlook/WebArchiveCopyPasteTempFiles/P698ojxP4tc7j8gMqgPv+E4KQAAAABJRU5ErkJggg==]<https://urldefense.com/v3/__http://illinois.edu/__;!ioFpBMP7lJU!kYg_ctrV6fkf5-Q0k15HPZw7eDzJHG_oXmJmgLbFYGCVB4UljJ9noqPPexT8GA$> > > Under the Illinois Freedom of Information Act any written communication to or > from university employees regarding university business is a public record > and may be subject to public disclosure. > > _______________________________________________ > LON-CAPA-users mailing list > LON-CAPA-users@mail.lon-capa.org > http://mail.lon-capa.org/mailman/listinfo/lon-capa-users _______________________________________________ LON-CAPA-users mailing list LON-CAPA-users@mail.lon-capa.org http://mail.lon-capa.org/mailman/listinfo/lon-capa-users
