[LON-CAPA-users] {Disarmed} Re: FW: Rounding Issue

Mills, Douglas G dmills at illinois.edu
Mon Sep 23 10:21:11 EDT 2019

I encountered this problem recently when testing to be sure that students were correctly entering the difference between two columns of experimental data.  My checking was taking place in JavaScript, not in Perl and I found this article to be very helpful for what I was doing. I'm sure this is not directly applicable to your situation, Gene, but nevertheless may be helpful?  I can provide more info on what I did and how my testing works if anyone is interested.



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 | dmills at illinois.edu<mailto:dmills at illinois.edu>


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.

From: LON-CAPA-users <lon-capa-users-bounces at mail.lon-capa.org> on behalf of Peter Riegler <p.riegler at ostfalia.de>
Reply-To: Discussion list for LON-CAPA users <lon-capa-users at mail.lon-capa.org>
Date: Sunday, September 22, 2019 at 7:35 AM
To: "Harding, Gene L" <glhardin at purdue.edu>, Discussion list for LON-CAPA users <lon-capa-users at mail.lon-capa.org>
Subject: Re: [LON-CAPA-users] FW: Rounding Issue

Hi Gene,

most likely the problem is one of number representation (which contributes to rounding errors).

The binary representation of $Av+0.05 is (by which I mean "the result of binary representation of $Av plus binary respresentation of 0.05 as a binary")


whereas the binary representation of 2.7 is


Both binary numbers differ only in the last two digits and the second one is larger. That explains why 2.7 is not accepted.

I have done the computations on  64-bit machine which likely matches your server's resolution.

I hope this is of help.

Am 22.09.2019 um 02:51 schrieb Harding, Gene L:
Hi everyone,

I have a quiz problem in LC that seems to be doing some odd things with the rounding. I have successfully recreated the problem reported by one of my students, but cannot figure out why it happens.

The answer to the problem (part c) is 2.65 on the dot. The problem requests an answer with one place after the decimal, and the tolerance is +/- 0.05. In this case, since the value computes to exactly 2.65, LC should take anything from 2.6 to 2.7. In fact, in author view LC indicates it will take anything from 2.6 to 2.7:
[cid:part1.99A52A7F.672D8F68 at ostfalia.de]

The trouble is that 2.6 works, 2.65 works, but 2.7 does not.

This is the Perl script calculation (Rf=33, Ri=20):
$Av         = 1+$Rf/$Ri;           # Gain

This is the response code:
<numericalresponse unit="" format="1f" answer="$Av" id="3">
        <responseparam name="tol" type="tolerance" default="0.05" description="Numerical Tolerance" />
        <textline readonly="no" spellcheck="none" />

Any idea what the problem is? I am baffled.

Best regards,

Gene L. Harding, PE
Associate Professor of ECET
Purdue University


LON-CAPA-users mailing list

LON-CAPA-users at mail.lon-capa.org<mailto:LON-CAPA-users at mail.lon-capa.org>



Peter Riegler

Fakultät Informatik

Ostfalia Hochschule für angewandte Wissenschaften

- Hochschule Braunschweig/Wolfenbüttel

Salzdahlumer Str. 46/48

38302 Wolfenbüttel

Tel 05331 939 31540

Fax 05331 939 31542

Web www.ostfalia.de/pws/riegler<https://urldefense.proofpoint.com/v2/url?u=http-3A__www.ostfalia.de_pws_riegler&d=DwMD-g&c=OCIEmEwdEq_aNlsP4fF3gFqSN-E3mlr2t9JcDdfOZag&r=d6Snpw24IWBdGQpe7yVTtlsEXqfulT1FGlRs-RT3y9s&m=lNqg2OTmaYK8aMffQM-PWQXcFIk8OeCaYOBvj1cHHZA&s=zEp_gv4MSfwthw4VS8lD3vtw2EEyoA4XJmiQK8H2rFQ&e=>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.lon-capa.org/pipermail/lon-capa-users/attachments/20190923/cea6a74d/attachment-0001.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image001.png
Type: image/png
Size: 2604 bytes
Desc: image001.png
URL: <http://mail.lon-capa.org/pipermail/lon-capa-users/attachments/20190923/cea6a74d/attachment-0001.png>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image002.jpg
Type: image/jpeg
Size: 4326 bytes
Desc: image002.jpg
URL: <http://mail.lon-capa.org/pipermail/lon-capa-users/attachments/20190923/cea6a74d/attachment-0001.jpg>

More information about the LON-CAPA-users mailing list